Ha, seems I'm the only other one here who understands what AA and AF are...
I have a 128 meg Ti4200, slightly overclocked. AA at Quintex and AF at 4x, and LOD at -2.5 I think. I run 1024x768 with all details on highest, frame rates run either at 30 fps, or at my cap of 50 fps (oddly enough, never in between ??). Snowy Park is the only place that the fps ever drops below 30, and that usually happens when I look up into the falling snow.
As for a recommendation, if you decide to buy, give Aopen a chance and grab their Ti4200 FAST version from
http://www.newegg.com I bought it for a clients computer, and although I haven't fired it up yet (waiting on a few parts...) it has some impressive stats. It comes with 3.6 ns RAM, and the RAM comes clocked at 550mhz, and should be able to go higher. And it's priced at 150 bucks.
However, the gap between your card and the Ti4200 isn't huge. Depending on what your cpu is, the upgrade may not be worth it. Chances are your processor will have more effect on performance then the vid card. But I dunno your whole system, so I can't make that call.
EDIT: OH, and btw, you realize that 4x AA is the highest the Nvidia cards go right???