here it is! the one and only CloneKeys, a program that broadcasts the keystrokes to two windows!
download it Here
Instructions for use:
1. Start up multiple copies of your favorite game. (Say World of Warcraft)
2. Start up CloneKeys
3. Click Add button in the CloneKeys toolbar.
4. Click a World of Warcraft game window
5. Repeat step 3 as needed
6. Play