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I wanted to find a way to disable the start menu popup but still leave shortcuts like Win+R and Win+L enabled. I messed around for 2 hours trying to figure out a solution and finally stumbled on a 2-line solution:
~LWin Up:: return ~RWin Up:: return
This seems to work on both XP and 7. Haven't tried Vista, but I don't see any reason it wouldn't work.