I'm Learning to Swim
It just takes time. I think most of us were in your situation at one point. Get in the pool every other day and just slowly increase your distance. I liked mixining up a length of breaststroke with a length of freestyle, a kind of active recovery. That way you dont stop swimming, but you do get some air back inside you. Steadily increase the ratio of freestyle to breaststroke lengths.
That worked for me, there are plenty of other opinions out there.
Brian
I remember just what you are talking about. This past February I started swimming (I had grown up living on the lake my entire childhood, and really enjoyed playing around in the water but I never really swam), in order to do triathlons. I was wasted after 25 yards, I'd have to hold onto the rail and rest, and then even then I was still tired when I started again. But I promise if you keep at it (especially if you have someone coaching you) it will get better. And it has almost nothing to do with what kind of shape you are in, because back in February I could run 10 miles at 8 minute mile pace no problem. A big part of it is being able to breathe comfortably, once you get that down and start to glide swimming becomes so much easier. I went from hardly being able to swim 25 yards in Feburary I finished my half ironman swim leg in 39:15 and didn't feel tired for my bike (I was sure tired of swimming, but I wasn't tired).
Just stick with it.

Hello once again. I am currently taking swim lessons just to imporve my stroke since Ihaven't swam in 5 years. Not bad, but not the prettist thing either. My endurance in the pool is not good at all in a 25 yard pool I can get about half way without having to stop to take a break. Does anyone have any workout suggestions to help me get back into swimming shape? Thanks