First thing I'd do, is get the config file from above (sanpei.org) and place it in /etc/X11/XF86Config-4. (Make a backup of your old one first perhaps). Then, type startx and see what happens. If this gives something vaguely useful (ie you can see something, but it's doubled up or too big), then either open up the file and change the sync rates manually, save and retry, or run (as root) xf86config.
After selecting the appropriate keyboard & mouse, try all of the available options with hsync between 31.5 - 57.0 kHz (at a guess), a low-ish vsync (say 50-70 Hz), and the Sis630 video card. It will probably save the file to /etc/X11/XF86config, which you will need to rename "XF86Config-4" (assuming you're using XFree86 version 4.x).
If you have a screen type toggle on your keyboard (mine is Fn-F5) then try pressing that a couple of times as X is attempting to run. This should switch between the available Bios options, which you can go back and change properly later, once all is up and running. Also, have a look at the man page (man XF86Config-4) - there's some useful stuff there. Finally, have a look at the log file (should be in /var/log/XFree86.0.log) - this may give some hints as to what's going wrong.
Anyway, I'm off down south climbing & tramping for three weeks so won't be back on this board for a while, but good luck with it all