OCModShop published a guide about speed up searches in Vista

Vista's search capabilities have changed a little from previous Windows versions, and is supposed to index files Instant Search is one of the best aspects of Vista because it allows users to hunt for files from virtually any location in the operating system; search boxes are integrated into the Start menu and into every Windows folder. It's a welcome addition, as it's faster and less intrusive than the standalone offerings from Google, MSN, or Yahoo, which were needed to scour your desktop in XP. If you start to notice that your index becomes sluggish in performance or even stops working, you can rebuild the index and regain the performance you seek.

How To: Speed up Searches in Vista