Just a thought: where was the software (eg Tom-tom) located? It has to be on some media that is recognized by WinXP. For example, if you are inside your WinXP session in VirtualBox and logged in as an administrator, and you setup VirtualBox to have access to the real cdrom drive, then putting a software disk in the cdrom drive should allow you access to the drive contents and clicking on the setup.exe should install the software. Or give an error message, just like in Windows on a physical machine.
Some software might not work in a VM (i.e VirtualPC), and it is possible that some installs might fail silently. Make sure it isn't one of those by installing something you know should work, like firefox, for example...