someone made a post about this...to build nvidia-legacy-drivers against the
2.6.20 you need to copy part of your original kernel and replace it into the
new kernel. can't remember what the file was called tho. btw it worked.
took a while, but i found it. David Baron posted it.
http://lalists.stanford.edu/lau/2007/03/0534.html
hth
g.