You'll probably find it easier to flash the Radeon 7000, due to a more standard design, and things like TV-out (if it has it!) should work. The Geforce 2MX will be faster, and things will seem a little smoother, especially Expose, from my experience. It is also a hotter running card. Not all GF2MX cards flash over though.

This site is useful:

http://www.cybercoment.com/macgeforce.htm

JB