It can be done, but you'll have to use the Terminal to do it. You should be able to get to the Terminal from the installer on the CD.
Once there, the command you want to use is this:
rm path-to-image
rm stands for Remote Mounter, which is the command-line method for mounting disc images in the Finder. Be very careful, though; it's rather finicky, and if you don't get the path exactly right you do risk some damage. Blame it on Apple's buggy software. In fact, it only works on images of bootable discs, such as the OSX install discs, and I very strongly recommend you not try it on any other kind of file. You risk real damage. But it works like a charm on install discs; I don't really claim to know why.
If this doesn't work, then I'm afraid you're going to have to buy another copy.
