Doesn't even have to be in windowed mode, though swapping takes longer that way.
There are also third party programs (which don't violate the EULA) which support the management of more than one instance of a game running on the PC. Just do a search for boxing s/w for more details.
Tat
Edited, Jan 11th 2013 11:18am by tatankaseventh
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Tatanka Wolfdancer, 115 Wood Elf Druid, 9 x 300+ Master Artisan, 7 maxed trophies (dang research! :)
Michone, 115 Troll Shadowknight
Anaceup Mysleeves, 115 Erudite Mage, 2 x 300 Master Artisan
Snookims Whinslow, 112 Erudite Enchanter, 2 x 300 Master Artisan
<Inisfree>, Tunare (Seventh Hammer!)