Thanks for your reply, looks like you were very right, see below.
Looking for "toshiba m10 geforce4 420 +northbridge" on the internet I stumbled onto a very good article on notebook graphics (ao). Unfortunately it is in French, but here is the link anyway:
http://www.tt-hardware.com/article.php?sid=4884
3D Mark 2001 results (from article):
IGP 320/340M: 1300 - 1800 points (depending on config)
GeForce4 4xx (420, 440, 450 et 488): 3700 - 7100 points
I guess there's no need to speak French to understand what that means!
By the way, what northbridge does your M10 have?