Removing cover from Dimension 4600

I bought an internal DVD burner for my Dimension 4600. I removed the side cover okay, but I couldn't get the rest of the cover off to get to the other side to remove the other screws holding the CD burner. It seems to be held on by a bunch of rivets. I removed quite a few of them but it was still on there pretty good. Am I going about it the wrong way? Sorry if this sounds like a stupid question, but can someone help me?