Have you tried un-installing "Visual Studio 2008 Express" from add-remove programs, the IDE for the Visual Studio apps is kind of seperate from the actual C++, C#, VB compilers. You can even download a Visual Studio IDE SDK from MSDN and make your own custom IDE using visual studio.
Basically when I want to un-install any microsoft stuff, which tends to be made up of multiple things, I go through add/remove programs and un-install any reference to it or anything it was dependant on(in this case the VS08 C++ express is dependant on the Visual Studio IDE). Once there are no references to the product inside the add-remove programs applet, its usually safe to delete the remaining files manually(as long as you have backups, sometimes microsoft's dependancies run deep).
I know that technically, the uninstall APP should go through and remove all traces of the app you want to remove, and usually they do, but there are some cases where either through registry alteration, or program modification from outside sources, later installs etc that result in the installer not doing everything it should.
EDIT : Be careful while playing with uninstallers that you dont accidentally remove your VC++ runtimes, as they are needed by a whole lot of stuff.... basically to run anything created in VSC++
If it ain't broke.... DONT FIX IT !!!