I'm about to build a 1.1-1.2 ghz Tbird system myself. I have about half the components now. (I've been picking off good/great deals, while waiting for the mobo situation to clarify.) I was waiting to decide between the KT133A, and the AMD 760 DDR mobos. I've just about decided to go the KT133a route, after Tom's Hardware joined AnandTech in opining that that is the smarter route for now and the near future, and after Tom's did a comparative review of a bunch of them. (The Abit raid KT133A board looks like a winner to me, edging out the Epox. And it's also available.) So anyway, I have had a similar quandry on the video card front.
I say definitely DO NOT go for a 64meg Geforce2. It is real diminishing returns land. Very marginal improvement over the 32 meg geforce2, and then only in the very highest resolutions, e.g. 1600x1200. Just play one notch lower, at 1280x1040x32, in games which tax and need the highest frame rates.
Then about 3-4 months after the nVidia NV20 comes out, and games are being released which really take advantage of its significantly new architecture, mostly because of the X-Box effect, THEN buy that card. NOT when it first hits. Because of X-box, that card looks to be a real quantum leap. But not until games are writing for it. X-Box comes out in the fall. Which means that is the soonest you should be thinking about an NV-20 card, if you ask me. More likely about now a year from now.
I also strongly considered the Radeon 32meg DDR route. Cheaper. From what I can tell though it really doesn't look any better, except perhaps in playing DVD's (which I do on a seperate DVD player hooked to a big screen TV anyway). eVGA has a Geforce2 GTS with TV out for only $165. You can find it on pricewatch. That particular make/model of card has also gotten a strong review. It's getting down close to the Radeons. I've about decided to go that way.