I recently had to install Redhat 5 and Centos 5 on a few Dell machines. I was installing these on a Dell Dimension 3100s, and ran into a problem during install.
I was installing on over the network with NFS, using a usb bootloader. As soon as the graphical install started, the screen just went black. Well, after scouring the internet for a solution, I finally came across the magic answer.
The trick was to enter:
at the boot prompt. Thats it, the installs both went smoothly from there on. Hopefully this makes it to someone in my same situation.