Microsoft released a download called Windows Vista Upgrade Advisor 1.0. This download will determine whether your PC is good enough, ready to be upgraded to Windows Vista. It also gives you the available Vista editions and features based on the computer check. Download size is 6.5 mb.

System Requirements:

* Supported Operating Systems: Windows XP Service Pack 2
* A minimum of .NET Framework 1.1 and MSXML 4.0

Official download page [Microsoft]