I like to use Linux on my computer but once in a while I want to use Windows for games. Is it possible for me to create an image of a Windows computer's hard drive, copy it to my main PC, and use the file as a boot device? How would I need to modify my lilo.conf to do this?

Well, aside from the legal issue of having 2 copies of your Windows install, I don't think it can be done. Your best bet is to create a small partition for Windows and to dual boot.

That's a common misconception - it isn't illegal to have 2 copies of your Windows install. What's illegal is to let someone install your copy of Windows on their computer. You can call MS up on the phone and ask them to give you an activation key for your second computer over the phone - I've done this before with Office. Wasn't very fun, though - if it were my PC I would've just got OO.o.

I think I remember reading somewhere that in Linux you can boot to a "loopback" partition which sounds like what I want to do - have the system pretend that the drive snapshot is a partition. But I don't remember where I read that.

But then you would need your snapshot to be a .iso file. Could you not use Qwmu or VMWare for this? Install Windows within that program and then run that from within Linux.

Having the snapshot as an ISO is not a problem for me. Since the computer will be using it as a hard drive, Windows won't know the difference.

And I don't have any virtualization software - I wouldn't really want it anyways. What I want is just a way to take my laptop's hard drive, copy it into an ISO file or something, and then be able to boot from that file.

I'd repartition my drive, but I don't want to cut off a slice of my HD just for Windows because, like I said before, I mainly use Linux - and if Wine worked with Steam better (or if the free version of Cedega worked at all) I wouldn't even need this image, and I'll probably just delete the image once I get Wine working with Steam.