Hi,
A quick/easy solution for when you are developing is to compile your debug version to the c:\windows\ehome directory (assuming your Vista is installed to c: drive) - this way you can avoid needing to register it with the gac each time. If you use this method - ensure you delete it prior to final/proper release (where you would then use a Wix installed to do the proper gac registration).
Alternatively - please look at the getting started docs in the 5.3 SDK which suggests the alternative way to compile (where the compiled dll is registered/unregistered) to the GAC each time you launch it for Visual Studio.
Niall