how do I fix xserver remotely?

[tripolar <tripolar@comcast.net>]

during an install on my parents pc I chose wrong xserver "fbdev" because I 
didnt know there video card at the time. since then I found out it was s3 
savage.
First I was locked out because of root password problem. fixed now with help 
from this list :-)
Their pc is running knoppix live-cd ( so she can access internet) while I sort 
this out. I will need to log in ssh ( not a problem did that earlier) and try 
to fix x by editing file and hopefully when she reboots after removing 
knoppix cd, gdm will start.
any clues would be helpful
thanks