failed vista sp1 install.

For the past month I have tried to install SP1 but anything I have tried has
failed. I have done everything listed everywhere to try and install.

I have uninstalled firewall & AV software, run the update readiness tool,
run sfc routine and every other check there is to validate the system
readiness.

I have run both Windows Update, the 5 lang and the ALL lang standalone
package and all fail at the same point. It gets to stage 3 or 3 100%
complete, hangs there for about 10 minutes and then comes back with service
pack did not install. When i get back in windows, the WU doesn't display an
error code but the other 2 packages show the error code: 0x800F0826

Numerous days of chatting to help and support has not solved the issue. They
have then told me to do an inplace upgrade and try again however, the upgrade
fails as well. everything runs smoothly until the second stage of the upgrade
"gathering files". That gets to 70% and then comes back with "windown
installation encountered an error and cannot continue." (I have followed the
tech support routine for the inplace upgrade - involves switching off some
services).

I have rebuilt the BCD from scratch.

Any ideas of what to do now or am i looking at a clean install?

The system is: Advent 8117 notebook, vista home premium, 120Gb HDD (62%
free) intel T2080 processor, 2Gb memory. All drivers for audio and video are
up-to-date. currently no AV or firewall installed (but not on net with it
while i install sp1)