I had already grauated, but took psych at the local community college to fulfill the pre-req. If it's listed as a pre-req for the school you have to take it. It's very rare that they wave a pre-req. The only cases I've seen that they've done that is if you take a class that's HARDER or of a higher level than the required pre-req.
But call the school to find out which community college they recommend if you're going to take a night class. Some schools look more favorably at one college than another.