the last few weeks because while getting the system up and running (drivers, resolution, etc.) I've broken something (X, grub, unknowns) and I can't get it back to work.
Especially for a newbie like me, it's easier (and much faster) to just reinstall the whole shebang than try to troubleshoot several layers of failed "fixing" attempts.
Coming from Windows, I expect that there is some "disk image" utility that I can run to make a snapshot of my Linux install (and of the boot partition!! Then, after I've foobar'ed my machine, I would somehow restore my machine back to that working snapshot.
Torben, under the Wubi folder (usually C:\UBUNTU, but may be some other drive & folder), you'll find not only the loopback disk images created for your Ubuntu install, but also some other important files (like the Wubi loader).
Sorry if it's a guess, but I think it's an educated one.
;-) Maybe ('cause I really have never tried - sorry - but wouldn't hurt if you try it - I would) if you backup that folder while the system is in a good state, you can take Wubi back by replacing the good state over the non-functional one.
Please post this as an answer, because it sounds like a good way, specifically for Wubi installations!
And a great way to create one is the Linux Live USB Creator.