Run Script Before Starts (before Welcome Screen)

I am planing to reformat my laptop and I am going to partition it so that I have one maybe 5 GB windows partition and another partition for everything else. When I say everything else I mean Program files, documents and settings, everything not in the windows folder basically. I want to do this so that if I were to defragment the windows for faster booting it wouldn't take too long. Also if i were to reformat then all i have to do is reinstall windows on this partition without loosing anything. Anyways so I figured in order for me to do that i would have to mount Program files and Documents And Settings from my 2nd partition to the folder c:program files and c:documents and settings.I would have to do this before i see any gui of windows I suppose. (Not sure if the welcome screen looks at logins based in documents and settings or not) but either way i would need it to be mounted and ready for use by windows.

So how would i execute a script before windows starts? Also how do i use mountvol to do this (no matter what parameters i try nothing happends(doesn't even give me an error just gives me the "help" display))I for some reason cannot mount a folder to another folder on another drive but i'm thinking i can use the subst utility to mount a folder to a drive and then use diskpart to mount that drive to a folder but i don't want to use diskpart so much because it needs me create a separate script file for me to run it with a script, so i want to use mountvol which supposedly does the same (according to microsofts website)