I think each sprint that happens in a pool may not be the same. The one I went to did a serpentine through the pool. You went down one side of the lane, came up the other, then went under the lane line and went down one side, came up the other. You went through the whole pool like that, which ended up being 300 yds. I didn't see people tapping people on the toes when they passed them. They just passed the person. Also they lined us up according to our times and then let someone go every 10 seconds.

I saw a variety of different outfits. Some people wore trisuits and some wore jammers. To my knowledge, no one changed per say. I threw on a set of bike shorts and shirt over my suit - which really isn't a great idea because it just adds time on. My transition time was just over three min. but could have been much less if I wore a tri-suit. That was my first one also, so I was there to finish and basically see what happens and what I can do.

Your first question and the first part of your third question should probably be directed to the race coordinators. If they have a website or a contact number you should contact them. Not every sprint is the same. They should line you up or group you with people that have similar times but again you will need to talk with the race coordinators to find out how they are setting that up.

Good luck and have fun!!

Normally, they do the serpantine swim (either up 1 lane, under the rope and down the other OR up and back one lane...under the rope, etc depending on the distance). Pass people on the left and otherwise stay to the right of the lane...same as swimming w/ a team. They'll start people every 15 or 20 seconds usually. Very few people will be in correct order according to speed, so expect it.

I have seen a variation where you stay in the same lane...it is done with heats and usually like 4-5 to a lane...but seems confusing to me and is much less common.

And then there is the TriforJoe in Cincinnati, where they setup a strange "buoy-style" configuration in a pool and treat it like an open water swim...which is rarer still.

If I had to put money on it, I'd say serpantine is what you'll have. I find it has it's own frustrations compared to OWS, but is a lot less nerve-wrecking especially for weaker or newer swimmers since you can see under water well, you start with your own space, and there are walls and shallow ends

Typically, you will circle swim (go down and back on the right side, much like driving). You will be paired up with a few people of the same ability in the same lane. It helps to know very closely what your time will be for the given distance, as this assits the coordinator in defining lanes. If you under/over shoot your time, you will either be tickling peoples feet in order to tell them you want to pass, or you will have your foot tickeled (sp?). You will be lined up in heats depending on how the race coordinator wants to do it. (Typically, the fastest men will be last).

For attire, tri shorts, jammers, tri-suit (not a wetsuit) or skinsuits are the norm. I go with jammers, since i dont have tri shorts and my bike shorts would create too much drag, and my tri top.
Depending on the weather, you may want to have an extra long-sleeve top available in transition for the bike.

Good luck and Rock on.

1. As has been noted, a pool swim probably guarantees serpentine.
2. People will be wearing everything from trisuits (NOT wetsuits) to old-school Umbros. No, you won't change clothes in the traditional sense of having a tent or something. Remember, there's a clock. Generally for a sprint, you can get away with a trisuit from start-to-finish. If you don't have a trisuit, swim/bike/run in your cycling shorts. No biggie.
3. If you are are planning on a 7:00 to 8:00 finish for a 250m swim, uhm . . . there probably won't be anyone behind you. :) Anyone back there shouldn't be annoyed becuase they're no Phelps either. Not trying to be a d*ck, but you'll be waaaaaaaay in the back of the 'serpent' with people who may try to walk the swim, so don't worry about it. And yes, people will walk the swim (assuming the pool is shallow enough).

Usually when I do pool tris, they fit up to 5 or 6 people in a lane, usually with circle swimming (up one side, down the other). If they do two per lane, it is often the case that each swimmer gets their own half of the lane. I wouldn't worry about slowing people down. They should seed you based on a time that you predict you can swim. If you are in a lane with faster people, expect a toe tap when they catch up to you and want to pass. The best thing you can do at that point is swim close to the lane line and they will pass you down the middle of the pool. If they don't take the cue, you may want to take a quick stop at the end of the pool when you reach it to let them pass.

If I am doing a pool swim, I will usually wear my tri shorts (they are basically a mix between bike shorts and jammers). Some people race in trunks or fancy fast-skin tri suits. Its about what you can afford and how competitive you are feeling. I also wouldn't worry about changing. Before I got my trishorts, I swam in my swimming speedo and then did the rest of the race in it. I got a lot of whistles, but hey, might as well show off a little.