The other NIC is probably disabled in the BIOS.  You can use OMSA to check/enable, or you can boot to the BIOS Setup (F2), Integrated Devices, and enable the other NIC.
Wiped/loaded PE1850 w/ Server 2008 R2 and only 1 NIC showing in Device Manager. The back of the server has 2 NICs as indicated in this picture. Any help would be much appreciated
PE1850 w/ Server 2008 - Only 1 NIC showing