Sure its possible. I do it using 1 keyboard and 6 wireless adapters when playing EQ2 or 5 when playing WOW. For key strokes and mouse clicks it works great. For mouse movement not so good. The cursors all move in the same general direction, but exact locations vary.

When playing EQ2 I use the mouse to click, I prepostion the cursor using another mouse attached to all the computers through some KVM switchs. Then click the wireless mouse for a simulateous click. In WoW you can map a keystroke to the mouse click so I dont' use it.

I use a Logitech S520 desktops, I got a good deal on them at the time. I don't think this model is around anymore. But any of the Non-Bluetooth models should work. The Bluetooth models will mate the keyboard to a receiver so you will not get a broadcast effect with them.

I have all my machines running Multiplicity so I can move the primary Keyboard and mouse, easily to any of the computers for individual attention.