That thread refers to FreeBSD 7 and 2.0rc1 is based on FreeBSD 8.1.
You are already running a more up to date driver than that.
You can see which driver you are using by viewing the sysctl:
[1.2.3-RELEASE]
[root@fire.box]/root(2): sysctl dev.em.1.%desc
dev.em.1.%desc: Intel(R) PRO/1000 Network Connection 6.9.6
I am running 1.2.3 on this box as you can see. You will have the legacy driver, which is newer! ::)
Steve
Edit: Finally found a good explaination. From version 7.0.0 of the driver the code was seperated into two em and lem, although you won't see that as an end user. The lem driver is for legacy adapters, which is anything pre PCI express.