Well, AutoC2D does what the name implies: it Automaticaly moves Program Files from C to (2) D. Theoretically, after running AutoC2D, everything should work just as before, and you'll have alot more space on your C drive. How does it work? Well, here's the process:
(1) When running AutoC2D, make sure you have no unsaved work or aren't playing a game, because it will reboot without asking you.
(2) Once rebooting, it will automatically start into Safe Mode, which is a mode where only the bare minimum of programs will be run. It does this so it can free up every file in the Program Files folder.
(3) It will automatically start copying from C:\Program Files to D:\Program Files.
(4) It will reboot, out of safe mode.
The way AutoC2D "switches" everything over is that it not only moves the files, but it also creates a Junction. A Junction is a folder that is not really there, but points to another folder; like when you click C:\Program Files, it just takes you into D:\Program Files. It basically allows files to "exist" in two places at once, but only taking up the space of one. That's a pretty terrible definition of a Junction, so please search around for someone smarter than I, if you want to get into Junctions and whatnot.
There's a few things I've noticed about AutoC2D (since I've had to use it several times...):
Creates temporary files: After moving, I found a folder with alot of files that looked like they belong in Program Files. It's not a big deal, since you can just delete it, but I don't know if it's a "backup" folder, or maybe a "mid-move" folder. I just wish ASUS would've said something about it.
Had trouble with safe mode: I really don't know if this was just on my computer, but I had trouble with my Eee being stuck in safe mode afterwards, which was very frustrating. I did end out getting it fixed, but it made me very cross at AutoC2D. That being said, that was the first time I used it, and the other times, it worked wonderfully.
AutoC2D is fairly small, and must be installed.It is not portable because you need to download Windows Server 2003 Resource Tools, which I'd never even heard of before getting an Eee and AutoC2D.
The thing about AutoC2D is that it is basically a tool to make your life easier, and it does that by doing several steps with no human interaction. But you can't do it manually as well, if you want.
If you wanted to manually pull a "C2D", all you need to do is boot into safe mode, move C:\Program Files to D:\Program Files, and create a junction. Of course, most people might be afraid when I say "create a junction", but it's actually quite simple if you use a tool like Link Shell Extension, which practically makes it as easy as making a new folder. The plus to doing it manually is that you can select someplace other than D:\Program Files. But if you don't really care and want to just be able to run a program, walk away, and come back with all your programs moved over, then AutoC2D will definitely make your life easier.