Mike, do you have your data backed up? If not, now is a good time to do so. A Puppy Linux Live CD should allow you to do this.
See this post by Happyrck in GeeksToGo: Use Puppy Linux to backup your data
Get the latest Puppy Linux listed, not the one Happyrck mentions as it's no longer available.
Once you have that, boot the Windows XP CD. At the first opportunity, enter
R to start the Recovery Console. It says Repair but that is an unfortunate choice of words by MS, that has confused many people over the years. When you get to the Command Prompt, type
chkdsk /r and press
Enter. It will take quite some time to finish but let it run undisturbed until it does. Try booting Vista now, see what happens.
If that doesn't help, you can try wiping your hard drive and doing a clean restore or install of Vista. There are lots of tools available to do this, but
DBAN is one of the best.
It's also possible you are having a hardware problem. If so then none of this will make any difference, except backing up your data so there is no chance of losing it, no matter what happens.
Before you go wiping the hard drive, try stripping your computer down to the bare minimum by removing everything you can, leave just the mouse, keyboard, one stick of ram (remove any others temporarily), any expansion cards. Leave just the DVD drive (if you have more than one, disconnect the 2nd one). Unplug all USB devices, flash cards, printers, scanners, etc. Now try the recovery and Vista Home Premium discs.