Depends which GeForce 4 you're lookling at. A Ti200 has DX8 feature support unlike the GeForce 4MX series, But A GF4Ti4200 has everything the Ti200 has, just faster. If you have a Ti200, and some extra $$$$ I'd advise keeping it until september and getting an ATi Radeon 9700, which is MUCH faster than a Ti4600 (35%), but it will be about $300. If not, keep the Ti200 until the GeForce 4 Ti 4400 get cheaper ($175)
EDIT:
Here's a list of cards in order of speed slowest --> fastest with prices in parentheses
GF4MX420 (60)
GF4MX440 (80)
GF4MX460 (130)
GF3Ti200 (105)
GF4Ti4200 (140)
GF4Ti4400 (225)
GF4Ti4600 (300)
All of these prices are from
http://www.newegg.com the best place for computer parts.