Tyco

My specs:

Gateway 500XL
512 MB RAM (two 256 MB cards, with two empty slots)
2.60 GHz Intel Pentium 4
NVIDIA GeForce FX5200 (128mb)
80 Gig HD
200 MHz Intel motherboard
Creative SB Audigy 2 audio
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For Christmas, I'd like to upgrade my GPU, and possibly my RAM to 1 gig. What sort of GPU would be the best for around $150? If there are some good ones cheaper, that's even better. I'll be playing lots of kinds of games, but mainly Flight Simulator X, Doom 3, and probably more graphically intense ones after I buy this new GPU.

Thanks!