Rent it. You might be miserable on the swim in a tri suit, but you'll DEFINITELY be miserable on the swim in a regular wetsuit.

The tri "requires" a wetsuit? Read carefuly. I've never heard of a race that requires one. Granted, I live in Texas, so it is possible, I guess. They are usually optional if the water is "cold," so be a bad ass and don't use one. You'll T1 faster. It is usually the case however that triathletes look for excuses to wear them, like "Oooooh, 72-degree water! I'll die. Must have a full!" So USAT and IM have rules that say they CAN be used if the water is below 70-something. I'd be curious to know what race it is. Care to share? But to answer your question, yes, a diving/recreational wetsuit is WAY different than a tri wetsuit. The difference lies mostly in the shoulder areas and the legs. The shoulder areas have elastic and webbing to help with strokes, and the neoprene in the legs is thicker so they float more (and you don't have to kick as much). If you really do need a suit, like the water is 50 or something, rent one. I bought a $300 suit and have used in three times maybe in four seasons.

EDIT: Word of advice! Learn how to put one on and take it off! They are easy to tear and I imagine you'll be charged for tears if you rent it. How do you put one on? I put plastic grocery store bags on my hands and feets and THEN slide the wetsuit on. It helps the feet/legs/arms slide through the suit. Also - I promise you will do this - you will put it no backwards teh first time. The zipper goes in the back. That long cord is a zipper pull extension so you can reach behind you and pull down the zipper. Also, the minute you get it zipped up, you will have to pee. Don't take it off. Just pee in the suit. It feels great, especially if the water is cold. And finally, get in the water early, fill the suit with water by pulling open the neck, and fill the suit. You need a few minutes to heat the water with your body temp. That is why they are 'wet' suits and not 'dry' suits.

I contacted the race director for my first tri because the rules said a wetsuit was required. He confirmed that the coastguard or whoever controls Lake Erie required it. I have a hard time imagining that if someone couldn't keep their head above water, a wetsuit would save them. I understand it makes you more bouyant, but it doesn't seem like it's enough to save someone.

TryScott is right. You can either swim or you can't. A wetsuit won't save you. That's not what they are designed for.

Well I'll be dammed. I was certain that I would NOT find a race in Utah that REQUIRED a wetsuit. But the Salem Spring mini in Utah - in June - does say that "Utah County Search and Rescue will be monitoring the swim and as such is REQUIRING wetsuits for all competitors." Well, screw me. I still think, however, that a wetsuit for an 800m race is overkill and a race should not require something that most races deem as optional. And if the water is so cold that search and rescue require wetsuits, you probably shouldn't be racing in it. So how cold is Salem Pond? The best I could find is the average temp is somewhere in the 60s. So swimming 800m in 60deg water is killer cold?

http://www.waterquality.utah.gov/watersheds/lakes/SALEMPOD.pdf

Also, I looked up the requirements for the Escape from Alcatraz tri, which I think is widely noted for having 55-degree San Francisco bay water. They "recommend" wetsuits for a 1.5mile swim with sharks and currents.

http://www.escapefromalcatraztriathlon.com/Race_Info/course.htm

I find this amusing, namely because the minute the news goes out that wet suits are allowed, you have the majority of people who own them suiting up. Why do you suppose this is? The advantages of the wet suit are fairly well documented. There is less drag. You are more buoyant. Your body stays on top of the water (water has 1000 times more drag than air), thus swimming requires less effort. You do have trouble, its easier to float with minimal effort. It keeps you warm.

Now, whether or not that adds up to the "slower" T1 time can be debated. I swam in 70 degree water in October without a wet suit just fine. I saw people coming out of the water at IM FL 07 that were blue with wet suits. If you are going to swim in water below 70 degrees without a wet suit, you'd better know what you are doing.

I wore a wet suit in my first tri in Atlanta on May 5, 2007. The shock of hitting the water, even with the wet suit, drove all the air out of my body. Thank God it was a newbie tri and we were swimming along the shore. I would've been in real trouble. That's probably why they require wet suits, to keep all the new tri athletes from shocking themselves and drowning.

Just my opinion :-)

My hat goes off to anyone who would want to do Alcatraz w/o a wetsuit.

And as for the T1 time... REALLY??? Because I know when I am flailing about, and gasping for air in 65º water, I'm totally thinking, "... but my transition is going to be killer!".......

O.K. what about this for a crazy idea? I do have a shorty wet suit, but like my long regular wet suit, both are restrictive in the arm/shoulder area. Is this a stupid idea-- cut off the arms of the long wet suit? Make a sorta wife beater type of top out of it. One of the downsides I can think of is that there wouldn't be much of a water seal, if any at all around the armpit area. It might look kinda stupid too. It is not an expensive wet suit and I really don't see using it in the future. I could sell it on ebay and put the money toward a real tri suit. I do know that putting that wet suit on and especially trying to take it off is a huge pain. Do most people have a helper at the transition to peel their wet suits off? My shorty is a lot easier to put on and off. I looked at the pictures online of last year's race and of approx 80 entrants, I saw only one guy who was not wearing a wet suit. It must have been a cool day too as on the bike ride, most people looked to be wearing long sleeve shirts or windbreakers.

I'd say don't ruin your full wet suit even if you aren't that attached to it. I imagine it would be cheaper to rent a tri-specific than to chop up even a cheapie.

Take the wetsuits that you have to the pool or to the lake and see just how uncomfortable they are to swim in and just how fast you go. If you can do the distance all right, no reason to worry all that much for your first time. Plus, you have to have somewhere to go for your second, third and tenth races. Save the unveiling of your cool new tri-specific for a later race.

Having given that advice, remember that I'm the guy that shows up to the race not only with his shorty wet suit, but also with his mountain shoes and mountain helmet complete with visor. I also take time at T1 to put on socks and sunscreen and time at T2 to take off bike shorts and put on some meshies. Now that you know what kind of hack you're dealing with, listen to the other guys who are the real triathletes.