I haven't tried all simulators on the market, but Realflight G2 would be very good. Works very well on my XP-machine with PIII 850 Mhz and good graphic card. Not the cheapest one but one of the best.

I flew a lot when I was 13-18 years old but didn't start again until 35. I could promise you that I'm a much better pilot now after a lot of G2-hours and some flying with a trainer. My second plane is a Sig Somethin' Extra.