I just noticed Jan pointing to a great little tip for adding DLLs to the GAC
Add following text to a .reg file, double click it, voila: you can add assemblies to the GAC with only two mouse clicks! BizTalk and SharePoint developers will love it. Check out the BIA blog post to download the .reg file in a zip.
Windows Registry Editor Version 5.00
@=”c:\\windows\\Microsoft.NET\\Framework\\v1.1.4322\\gacutil.exe /i \”%1\””
Note: This still doesn’t mean the web parts “should” be installed to the GAC