The problem with trying to transfer the OS is that the drivers would not work. It is possible, sometimes, to transfer from one system to another, though. I used to have a link to a good article on it, well about changing motherboards without reinstalling (same thing). You could Google for it... seems like it was a PCWorld article.
If you can find the article (or another like it), you could try it and see if it works for you. if it does, you would still have all of your programs and files "as is". if you Ghost it to a bigger drive (before or after, but before would preserve it just in case), you would have it all plus more room.
*EDIT* - Not the exact article, but I think it has the same info.
Beginners Guides: Upgrading A Motherboard Without Reinstalling - PCSTATS.com