Isn't that what the "Run..." option is for in XP? If so, I know Vista and 7 have something similar, though I don't remember where or what it is called since I don't use those systems much.
Sorry, missed the hotkey request. The windows hotkey for this is Win+R. See? Already built in - no extra resources. Now FARR is great if you want to extend that, but for this single snack, Win+R works great.