When I try to install guest Ubuntu 7.04 in Parallels Mac 3.0, I insert the disk as requested. An Ubuntu page comes up. However, the Mac then freezes and tells me (in four languages) that the machine must be restarted. After that I am back to square one. I have twice carefully followed Parallels's detailed instructions on de-installation and re-installation to no effect. OS X is 10.4.10. Thoughts?