I haven't started my 2yo daughter yet, but we have her signed up for Lifetime Fitnees on MOPAC in south Austin. I think they have a north location as well. It's an 8 week course with 30 minute classes.
We have a two year old and enrolled him at Emler's on Anderson Mill about a month ago. Good school so far. Emler
We just got some info on Infant Rescue Swim in the mail(sounds like your might be a tad old for this one) They're located on Anderson lane. Looks like a great school as well. Infant Rescue Swim
We took our daughter to Tom's Swim and Dive at 2222 and Burnet. They only take 5 kids a class so each kid gets plenty of attention. I highly recommend them.