Be sure you're not burning ISO's of ISO's... I made the same mistake a couple weeks ago. If you're using Nero--refrain from clicking the "ISO" tab--because basically, you'll be burning an ISO of an ISO. Instead, Open/Select the ISO file, and select burn--it should show up as either a data/CD Image--can't quite remember.
And to save yourself discs--burn only the first disc--check to see that it works (ie it goes to the Installation Screen post-boot up), and then reboot to burn the rest....