Problem with video on Dell 5150 and Fedora 15

[Pat Swayne]

I have been successfully using Fedora 13 and 14 on a Dell 5150 (with 
Nvidia Go5200 video card) for some time. I recently tried to upgrade to 
Fedora 15, and now video (after login) does not work. Fedora is the only 
OS, so I don't get the GRUB screen. How can I change runlevel, and what 
are some suggested changes to make.
If I can't get it working, how can I go back to Fedora 14?