Yes! Connectify Hotspot runs on Windows Vista and Windows XP. You will need the latest service packs: SP2 for Vista and SP3 for XP. However you'll find that not all of Connectify Hotspot's functionality is available - you can only operate in Ad-Hoc mode. Unfortunately, Windows Vista and Windows XP do not support Access Point (AP) mode. Microsoft has also made it clear that they do not plan on offering AP mode on either platform (XP/Vista) in the future. If you need AP mode you will need to upgrade to Windows 7 and have a Windows Certified wireless card.
So I'm stuck with Ad-Hoc mode, what does that mean? What is the difference? See the KB Article below: