System Reboots Part 3, Choice Boot Normally Safe Mode

I've been trying for 2 days now to upgrade from Vista Business edition to SP1. The same thing keeps happening. I get through parts 1 and 2 ok, but when the system reboots for part 3, it reboots several times giving me the choice to boot normally or in safe mode, then eventually it stops rebooting and just goes blank. I can reboot successfully in safe mode but the installation of part 3 will ultimately fail (the error code points to not being able to install particular components as a result of being in safe mode) and the system has to regress to the original condition. I tried all the suggestions on the MS Vista upgrade trouble shooting site (as well as several other sites)- including checking for specific updates - none of which apply to my machine - at least that what windows update tells me when I try to install them, checked the disk for errors, and checked the memory for problems. I also turned absolutely everything no- original MS off for start up including antivirus and some other stuff that I have and the same thing keeps happening. Each pass, from upgrade install to fail, and regress back to original condition takes about 5 hours.

I'm running Vista on a quad core machine with 4G of onboard memory (even though Vista 32 can only use about 3 gigs) and a smoking video card so I doubt this is a hardware problem. This problem appears to be similar to the original 'endless reboot' problem that prompted the original halting of SP1 distribution back in the early spring - I thought that problem was fixed! I tried to get real time help from the MS site but got a message that there was a problem with the site. - Good Greif! This is probably the most frustrating MS experience of all time. With all due respect to the folks at MS, if it was your intention to have people to switch from Windows PC's to Apples or even Linux based PC's, I doubt you could have come up with a better plan. I've already switched two of my home computers to Ubutu!