The Ti 4200 is a worthy purchase, and if you check out Nvidia's web site they have an impressive new graphics rendering program that uses their Cg programming language. C for graphics has huge potential and was inevitably the next step for graphics, it allows major control on all levels of programing for graphics and reduces file size and looks truly amazing. And it's all real time (with the ability to be highly interactive), no preproduction and then rendering a static scene/video.
OK, that's my speil for CG, now back to the card, for your money Ti4200 is a great deal. Depennding on your needs the 64 Mb has faster RAM (barely) than the 128. But if you have a large amount of graphics, animation and editing going on the 128 Mb is worth the extra few bucks.
I highly recomend it, it has served me well this past month.