You may find that Vista's new Instant Search can sometimes get out of hand and slow down your machine. Temporarily disabling and then stopping the search service is one way to deal with this issue:
Set-Service wsearch -startupType Disabled
Stop-Service wsearch
You'll need to run this script with full admin privileges. To turn the service back on, try this:
Set-Service wsearch -startupType Automatic
Start-Service wsearch