There is an option during install something like "Do you want to start XFree at boot" or something of that nature ... I always select "no" or you can just install with what you are most comfortable doing and if you can get a GUI to start up - then the easiest way to turn it off would be in Mandrake Control Center ... Boot Options.

Mandrake Control Center (hardware section from memory) will also let you test different settings and drivers for your monitor - if incompatible they should drop you back to the setting you had before trying.

With the troubles you describe I would be inclined to start afresh and do the re-install from the beginning and work slowly through it - from memory I think the installer allows you to keep the partitions you have already set up so you should be ok - but I dont think it will necessarily speed the process up a great deal.

Nvidia have also released there own drivers for their cards to run on linux, check out there site for details, the install process is very simple these days. Its been a while since I have run a nvidia card in my linux box but they do work quite well.

The file you need to pay attention to for you monitor is /etc/X11/XF86config-4, you may need to make manual modifications to this file if you upgrade to nvidia's drivers.

Again good luck.