There is a package I have to deal with which installs assemblies straight into the GAC (e.g. somewhere deep in %windows%/assembly).
How do I exorcise the actual as
I think the easiest way is to do it through the command line like David mentions. The only trick is that the .dll isn't simply located at C:\Windows\Assembly. You have to navigate to C:\Windows\Assembly\GAC\[ASSEMBLY_NAME]\[VERSION_NUMBER]_[PUBLIC KEY]. You can then do a copy using:
copy [ASSEMBLY_NAME].dll c:\ (or whatever location you want)
Hope that helps.