Have never tried to dual boot Unbuntu but have with Redhat and Suse. I guess it would all be just about the same.
Well, the ISO could be bad which would require you to download and burn again. Other than that. Have you booted off the cd-rom (Not using the live cd but using the text install) and proceeded with an installation from there.
I just read that Dapper Beta 2 just came out a couple of days ago becasue the beta 1 code possessed a lot of bugs regarding the installer.
See link:
https://lists.ubuntu.com/archives/ub...il/000072.html
Which could explain some of the problems that you are having. Personally, have not had a single issue wit hthe beta 1 cd.