Currently Being ModeratedMay 2, 2012 11:00 PM (in response to sydneyleb)
Configure your AEX to Extend your existing wireless. Run the Ethernet cable from the AEX to one of the Ethernet ports on your Mac Pro. Configure the Mac Pro's Network preferences to use DHCP.
Currently Being ModeratedMay 3, 2012 5:56 AM (in response to sydneyleb)
Kappy's instructions will work fine if your wireless network is being provided by another Apple router.
But, if your "main" router is not an Apple, you will not be able to configure the AirPort Express to "extend" the wireless network.
Instead, you will need to configure it to "Join" the wireless network and then enter a check mark next to the option to enable the Ethernet port during the setup for the device.