I would not suggest this as Windows Virtual PC does not support this. When the install of Ubuntu were to be complete in it, it would function in a very clunky manner with bad performance. I would suggest using VMware Player (
VMware Player: Run Windows 7, Chrome OS - Free Download for a Virtual PC) or Oracle VirtualBox (
VirtualBox) as they both support Ubuntu with their respective tools and integration components.
If you however still want to try this with Windows Virtual PC, you can just browse to Windows Virtual PC in your start menu and then click on it. After that, select the option to create a new Virtual Machine and specify where you want it to be saved and all pertinent options. Then just try to install Ubuntu but again, as I said before, I would not recommend this as it does not support it and it will not run all that well.