At

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dv_vstechart/ht
ml/vbcondeployinghybridvisualbasic60visualbasicnetapplications.asp

the short topic Add COM Registration for the .NET Component explains that you
can add registration using vsdrpCOM, which extracts into the MSI file the same
entries that regasm would create, so it just works. So you don' need regasm to
register .NET COM interop (I think VS runs regasm to get the registration data
at build time).

Gacutil isn't distributed with the runtime, so you can't rely on it being on a
client system. It was not in the 1.0 redist, but for some reason it showed up in
SP2 to the 1.0 redist, but it is not part of the 1.1 redist. To install
something in the GAC, right-click on File System on Target Machine in VS setup
project File System, and do the Add Special Folder. If you think that you need
to put something ion the GAC for COM interop, you don't need to. Maintaining and
updating new versions of .NET COM interop assemblies in the GAC is tricky. Just
install the assembly into the application folder, and you'll get the equivalent
to a regasm /codebase with no need to use the GAC.