I was trying to deploy a custom assembly today using Windows 2008 and SQL Server 2008 and found a bit of differences in Windows 2008. The GACUtil.exe utility has now moved first and foremost and is not installed by default until you install the .NET and Windows 2008 SDK. After that, you'll be able to find the GACUtil.exe utility in the SDK directory and can call it as shown below:

C:\Program Files\Microsoft SDKs\Windows\v6.1\bin\gacutil.exe /i "dllfilename.dll"

After then, you'll need to copy your DLL file into the C:\windows\Microsoft.NET\Framework\v2.0.50727 (or whatever .NET version you wish to be on) directory and you're golden to use a custom assembly in the Script Component or Task in SQL Server 2008/Windows 2008.

Brian