Power down the machine
Unplug the cable from the PSU
Open the case
Install the two cards
Install the Crossfire bridge
Plug in the PCIe power cables to the top of each card
Close the case back up
Plug the power cable back into the PSU
Power up the computer
Run the latest AMD CCC installer
Reboot
Open the CCC Control Panel
Select the CrossFire menu tab
Enable Crossfire
Then you should be all set
http://www.fighterops.com/forum/showthread.php?10351-how-to-setup-crossfire-ATI-Radeon-HD5770-1GB-graphics-card
Setting up crossfire is pretty much the same regardless of which graphics card model both (or more) of your cards are. It used to be a little more complicated than it is now, but not anymore. Multi-GPU setups are relatively easy to set-up.