The driver that is on intel.com, e1000e-1.1.2, is your best bet for reference code. The upstream drivers (in the kernel) will usually lag what you'll find either on SourceForge or intel.com for all of our drivers (igb, ixgbe, etc.). Just be aware the out-of-kernel-tree drivers also carry kernel compatibility code, which could be useful to whatever you're porting to, or it could throw a bit of confusion in.
What are you planning to port this to? We also have a FreeBSD driver for the same hardware.
You want the http://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&DwnldID=17509 Network Adapter Gigabit Base Driver for FreeBSD* 7.x. The list of supported devices for that download has been updated to include the Intel® 82573V Gigabit Ethernet Controller.