stuck half way through install

I've successfully installed Parallels Desktop 4.0 several times on my ibook and Mac Pro. However, this time on my Mac Pro it stops installing at various stages on the install.

I thoroughly cleaned the XP install disk. Any other ideas or suggestions? I've tried to install several more times. Each time it just stalls at various stages, usually in the second to last stage (installing extensions?)

Mac Pro 2.66, 6GB Ram, lots of HD space, OS 10.5.8