The Dell PowerEdge R300, as I found out today, has a NIC which is unsupported in FreeBSD 7.0 and earlier. The NIC in question, the Broadcom 5722, has had support added for 7.1 (not released as of this writing) and in HEAD. I found an incomplete walk-through for adding the patch for this card to 7.0 over at Hywel Mallett's site.
There are 4 patches to be taken into consideration. Mr. Mallett forgot to mention the fourth of these, which is what makes his walk-through incomplete. Being your system will not have networking support, manually add the following patches:
Here's the unified diff for your flash drive: Unified Diff