Alt-tab works for me with EQwindows without using the compatability toolkit. I thought EQwin was taking care of that issue for me...
BTW, the default binding for the TAB key in EQ is to switch targets between your current target and yourself (i.e. Targetting Mob, hit TAB, cast heal to heal yourself, hit TAB to target mob again and continue attacking). If you are alt-tabbing a lot, you may find yourself targetting yourself when switching windows (Me: "Why did my tank stop attacking? Oh, for some reason he's targetting himself now..."). I had to rebind this target-switch key to something other than TAB.