I recently upgraded to a T-bird 1.0 GHZ with a Abit motherboard from a
PII-450. Everything's great, just be prepared to add more cooling fans to
your case. And some heatsink compound...
I was debating the same card issues that you are. Then I found that you can
trade up to a 64 MB Radeon direct from ATI for around $160 after rebates.
You just have to (presumably) send in your old video card after you get the
Radeon. The reviews I've seen put the ATI card a little slower than the
GeForce, but the price looked to good to pass up. I'm also putting a lot of
faith in what Kevin Rice over at Daily Radar has had to say about video
cards and PC stuff in general. I've followed his advice in the past and
have been very satisfied.