Oh ok, I had assumed you were installing RH9 onto it
it could be any fault... if you interrupt Lilo, or grub when booting the machine, and put a 3 after the kernel, it should boot into run level 3, which should not boot X. This will give you the chance to fix the XF86Config file in /etc/X11/, to use the right driver for your new card.
Have you disabled the previous graphics card, if it was built in? I think you need to run xf86config (i think that's the name) to reconfigure the X system.
So, you should boot into runlevel 3, or disable the X server from starting up. run the xf86config and hopefully that should correct your problem.
Let me know if I missed something above, or if it's not clear enough. Even let us know how you get on!