Update:
So I just created 4 trial accounts, so you can do it. You can't make TBC trial account though unless you purhcase a retail copy of WoW. I inputed the exact same info for each account, but I just changed the account name xxxxx1, xxxxx2, xxxxx3, etc.

Seems like a great way to test your system before spending the money. Especially for all you out there that are asking if your system could support 2-5 accounts on one machine. I know this was a question for me, and now I'll be able to find out tonight!