i recently took the plunge and installed knoppix 5.1 onto my ageing tecra 520cdt, it sports 160mb ram 20gb ATA hd, and DVD drive and a whopping 166mhz MMX CPU

after initial boot up from hard drive it returns that the DMA is turned off (live CD boot showed ON, although i beleive this is a trait, will look into this as seperate post
http://www.knoppix.net/forum/viewtopic.php?t=29564
and screen size was 800x600 (HD boot gives 640x480)
in the inital grub boot where you see all the boot script displays as 800x600, the grub loader choice shows FB800x600 which makes sense, it then goes through probing the laptop finds the usual suspects all at 800x600, but when the KDM jumps in to run the KDE desktop it reduces to 640x480, where should this be changed? or rather which .conf has this data in it to crank the normal desktop upto a better res?
i assume xorg would change this?
i have had this installed previously on the same machine and the bootup found the video driver and its chipset and showed 800x600 and 640x480 as options, but on a subsequent install it fails to see the higher resolution
any ideas on what or where i should be looking