Please don't paint your pool. You're going to spend at least $500-600 on materials and you'll have to have it re-done within two seasons unless you really know what you're doing and buy the correct stuff. If the plaster is in even halfway decent shape just leave the surface alone.

I speak from experience. I spent $500-600 painting my pool and 2 days of labor and it was peeling by the end of the first seaon and we barely made it through season 2. I then had it professionally replastered for a cost of $2500 and the result has been much better.