Go into Disk Manager (Start -> Right-click "My Computer" -> Manage)
Click the "Disk Management" link in the left pane
Look for the new drive in the LOWER portion of the RIGHT pane. If the drive has no drive letter assigned (ie, "D:" or something similar), then you'll have to right-click it to create a volume and format it.
It wasn't showing up in Disk Manager at all. The drive was showing up in Device Manager, but uninitialized. So I took the HDD out of the enclosure and hooked it up to my PC as the sole drive and booted with a Windows 7 disk. I then created and formatted a partition on the drive. I replaced the drive into the enclosure and *poof* it works. Both eSATA and USb. I then used Disk Manager to delete the partitions (windows disk put a SYSTEM partition by default) and create a single partition. All in good working order!