You might check out
http://www.litepc.com/ if you are interested in reducing boot time.
The problem with converting a machine that has been used to exclusive MAME use is that you accumulate a lot of garbage in the Windows directory that you never even notice.
I'd probably just reinstall Windows from scratch, then patch windows, drivers, and such, then download any essentials, such as Winzip.
The cleanest way would be to transfer anything you want to save off the drive and then wipe it, but I'm lazy so I just renamed my Windows directory.
Buddabing