between ATI Technologies Radeon 7000 64MB ddr ram, and NVIDIA GEFORCE4 MX420 64MB sdram, which one should i get? both of them have the same price.

Definitely the Geforce MX420. You'll get much better performance in games.

but i heard geforce 4 MX is jusst a upgrade of a geforce 2. so what's the best graphic card in terms of price?

This is a link to the definitive answer on graphics cards. It compares all the graphics cards from the old TNT2, up to and including the geforce 4Ti. ENJOY

http://www.tomshardware.com/graphic/02q2/020418/