Problems installing Admin Tools under Vista? See this page. Microsoft have released a compatibility update but you will probably still need to apply the workaround (below and linked to on 4sysops) about registering DLLs as Administrator.

After installing the Server 2003 Admin Pack under Vista, the DLLs won't be registered correctly, and you will receive an error message in MMC. The following KB article provides a script to register the DLLs, which you will run as Administrator.