Yes (at least on XP, I can't test on Vista or 7, although I'd be interested to know if this works before I upgrade)
I wanted the opposite of your request i.e. Win-Tab (aka Cmd-Tab) to function as Alt-Tab. Phoshi's answer doesn't work for me, so I've added what does and also how to do what you originally asked
make alt-tab behave like win-tab
Here you go:
LAlt & Tab::Send #{Tab} ; this will make Alt-Tab function as Win-Tab
And the opposite:
LWin & Tab::AltTab ; this will make Win-Tab function as Alt-Tab
I haven't worked out ShiftAltTab or ShiftWinTab yet, but I don't use them as I tend to only switch between the current and last app in this way. I use Launchy on Windows and QuickSilver on the Mac for switching between many applications.