Onboard Broadcom® 5754 Gigabit Ethernet LAN solution 10/100/1000 Ethernet (Dell Optiplex 745 desktop PC) works fine (as of now) on H@ckint0sh OS X Lion 10.7 with your BCM5722D.kext.zip

ethernet:

Type: Ethernet Controller
Bus: PCI
Vendor ID: 0x14e4
Device ID: 0x167a
Subsystem Vendor ID: 0x1028
Subsystem ID: 0x01da
Revision ID: 0x0002
Link Width: x1
BSD name: en1
Kext name: BCM5722D.kext
Location: /System/Library/Extensions/BCM5722D.kext
Version: 1


Indeed the problem with your earlier revision lied in the upper case alphabetical characters in device ID string. They needed to be lower case.

Thanks a million times for your time and effort.