Getting ready to get my home theater set up..Using Pioneer FPJ1 Projector. I Have a lot of standard def movies. Should I buy a upconvert dvd player or just use my PS3?

The PS3 is supposed to be a pretty good upconverter if it has the latest firmware. Your projector should upconvert on its own as well, it's just a question of whether it or the PS3 does it better to your eyes.

You could also try a dedicated DVD player, but find one that you can return if you find it doesn't look any better than what you already use.