Does the hd4870 come with the bridge? I did not think that the 4870 had eyefinity. If he is running mulri-monitor with two cards will he still get the Crossfire power?
Most ATI cards come with bridges as far as I'm aware. They always came with ATI cards I've purchased.
2 monitor support for your desktop is not the same as eyefinity, which does need one of the 5xxx or 6xxx cards.
Also, Crossfire does not function in windowed mode. When he's using his monitors for his extended desktop, it will not be using crossfire.
Crossfire will work when he's in fullscreen mode playing a game. However, that fullscreen will only be 1 monitor, which ever is his primary display.