Vista - Vista Installation Hanging - Upgrade

I am trying install Windows Vista RC1 on a Dell Dimension 8100 desktop.
After converting the FAT32 drive to NTFS, I selected the Upgrade option. It
went through the following steps:

Copying Windows files
Gathering files
Expanding files
Installing features & options

and is now just stuck on:

Completing upgrade . . .

The 3 dots keep scrolling, so the machine isn't hung. But it has been doing
this for over 3 full days, so I highly doubt that it is going to finish.

If I try to cancel out the window, I get the message: "Setup cannot be
cancelled at this point. Doing so could leave your computer in a potentially
unstable state."

Does anyone know:

1) What to do with the machine at this point to avoid screwing it up?

2) What to do to get Vista RC1 installed in an upgrade process?