hi
first, during the installation of your 8.0, the X server worked ?
what config tool did you use to create the XF86config-4
I use XFdrake (be root to use it)
I know autodetecting the right card and mainly the
right resolution don't always work correctly, but you
can overrule it. Just say no, after you see the X-server
working with the tux wallpaper. Then you 'll be
back in XFdrake screen and you 'll see more options
Be right about choosing your monitor, then choose
your card and last choose your resolution and color-
depth (there 'll be more colordepth settings, at least
for my geforce gts )
when you leave XFdrake after confirming things work
the way you wanted it, typing startx should start your
X.
I think reinstalling won't be necessary
have fun