Thanks Zapdos
If you still want to try it, I would try the ASUS board. I looked at some reviews and it seems to be a good board from what I've read.
Just buy a board that you would buy if you were buying a new case. That might be what you will be doing if it doesn't fit, and there are some pretty good cases for cheap out there. You might just want to look into upgrading that way. It would be easier, and that is what I'm going to do with my Dell.