I am having a similar issue. Trying to install the ArcObjects SDK for .Net so that I can create an add-in from VB.Net. I am using VB.Net Express. I can get the add-in templates to show up in 2008, but not 2010. Do I need to uninstall 2008 so that it will install to 2010?
BTW, I had to uninstall/reinstall 4 times before I could get the templates to show up in 2008. I finally had to check the VCPP and Samples to get it to actually install anything even though that I am only concerned with the VB.
Edit: I am using ArcGIS 10 SP1