Just take off...
and nuke it from orbit. Its the only way to be sure!
Seriously though, I always install from a SA ISO and and add the drivers. That works with whatever product key you have, be it OEM, SA, retail, Action Pack. I've done that with Dell, HP, Lenovo, Asus, Acer and Tosh.
Finding the drivers is the pain. Tosh are the worst, their site is all over the place. At least with Lenovo you just need to install their 'System Update' utility which will detect your hardware and download all the relevant drivers (especially useful when there are 2 or 3 different cardreader/audio/etc used in a given model) and deselect what you don't want. Pity the other manufacturers don't have something similar. Combined with vanilla Windows install media it would make nuking and reinstalling windows much easier especially for home users (given all the dodgy sites that come up when looking for drivers).
(Note to self - get my own MDT instance setup soon!)