If for some reason you are stuck trying to run the latest Ubuntu (9.10 right now) on top of Microsoft Virtual PC 2007 SP1, you'll probably notice that while Virtual PC is a great virtualization solution for Windows and DOS, Linux isn't quite supported.
While earlier Ubuntu version had some issues just getting installed, you can just mount the 9.10 ISO file to the virtual disk drive and install the OS through the default installation process. As soon as the process completes, Ubuntu should be able to boot up (sometimes the reboot appears to hang — in that case just hard reset the virtual machine and Ubuntu will boot up).
Some features require some fiddling in order to work and — if like me your linux sysadmin skillz are pretty weak — the following instructions could turn useful. 
