Microsoft will begun pushing out version 4.0 of Windows Search, the OS-wide indexing system for Vista and XP users, via Windows Update in late July. If you're keen to get the new version before it hits Windows Update, which claims improved performance (especially on indexing of open email inboxes), you can grab a copy here. However, there's two potential challenges: it'll need to rebuild your whole index, which might cause system problems (though Microsoft claims any foreground activity will pause the indexing); and it won't happen until you reboot. If you've been there, done that and found Windows Search 4.0 a boon or a bore, let us know in the comments.
Reminder - Windows Search 4 coming to WU soon... [Microsoft Product Update Team Blog]