-I installed a fresh copy of Bitcoin-qt 0.6.3 on my secondary windows computer (.exe, not the .zip).
-Started it up
-Settings>Options>Detach database at shutdown
-Turned off Bitcoin-qt
-Deleted blockchain that had started to download
-Deleted my wallet that generated, and replaced with underworld's.
-I detached the database on my primary computer, turned it off, and backed up the blockchain (blk0001.dat, blk0002.dat, and blkindex.dat)
-Loaded those files onto second computer, then started backup bitcoin-qt on the second computer
The client crashed a couple of times while trying to start, and to had to forcefully kill the process twice. The UI splashscreen would crash everytime I tried to start it. It did it's normal "Loading block index" or whatever, and I did notice that it said something about "Rescanning...". Most the of the time though, it would just glitch and all I could see was a whitebox in the middle of my desktop. Anyway, after about 20 minutes of this, I finally got the client to start and load the wallet. I didn't shut it off until underworld gave me a new address to send to. I figured if I shut it down, I might not get so lucky and lose those coins. A couple hours after I got it working, underworld PM'd me an address to send the coins to, and I sent them. As of right now, I can start the client up, and it will load the address. I assume the client fixed the issue itself.
A clean installation seemed to do the trick. Not really sure how/why though. Glad it worked though. All-in-all, I spent a little over an hour while doing some homework.