sounds bad.

Go to blockchain.info and search for your mtgox transaction via either one of the addresses, or the transaction id, which you should be able to get from your client.

If the other amount to the weird address is part of that same transaction, then it was probably 'change' from the transaction coming back to a new address that was in your wallet.

If that's the case, you may have lost the key for that address when the wallet got corrupted in the crash, and so now the client can't see those coins as belonging to you. You may still be able to recover it from the corrupt wallet file though. Search around on here, there's info about how to do it. There's some tool you can download.

If it's a different transaction, then my guess is that your windows machine was compromised, and someone got your wallet passcode when you typed it in to do the gox transaction. They then straight away used it to get your coins. Is everything gone, or is it some weird amount? If there's anything left, I would guess that's not what happened. An attacker would take the lot.

I would never run a bitcoin client on a windows machine that is connected to the network and in active use. It's just too risky.

Hope you get your coins back.