Well, I figured that if it didn't work, my desktop could always use an additional drive, and it uses SATA, so it wouldn't have been a waste for me if it hadn't worked.
I grabbed a
DVR Expander drive. They're made by WD and seem to be pretty bulletproof. Fanless and silent, too. They do run a tad hot, though. Fry's had them last week for $129, which was cheaper than I could buy an internal drive with an eSATA enclosure to build something similar myself.
Funny thing is that when you call TWC, they will swear up and down that the eSATA port on the back of their DVRs doesn't work and that they cannot support the use of an external drive. But even in the manual that came with their DVR, it says that a drive can be added. I think they just don't want to have to support these expansion drives...or their gearing up to start offering them as rentals.