Messed with user acct name & now can't use new MacBook Pro I just received!

Question

I ordered a MacBook Pro 17" i5 for my sister off eBay that was only about 2 months old and seemed brand new. When it arrived this week I charged it up and then began tweaking the prefs and parameters for her, including some custom things and attempting to set up personal accounts for both of us. Since it was not brand new I didn't have to go thru the usual welcome & set-up process. The seller had a generic name "macuser" as the sole user account with no password. When I went to set up the user accounts in the system prefs pane, I foolishly changed the user name from "macuser" to my chosen personal name. It confirmed all was changed successfully, but upon logging out and then attempting to restart it just hangs on the gray apple startup screen indefinitely. In hindsight, I realize I should've created a new user name and then logged in under that and only then deleted the original "macuser" name (although I'm not sure why it let me change the current one "successfully" if that was going to be an issue). I could've duplicated the user folder, named it what I wanted, then when I went to create the new account in system prefs it would ask me if I wanted to use that folder for the new name that it found.
The seller did not have or include any of the restore/install DVD's and I don't have a copy of Snow Leopard (still using Leopard on my MacBook Pro 15") to boot it up with. I'm sure it has to do with directory issues and the system now confused by the new user name created from the old one in this unclean, sloppy way. I tried rebooting in "safe mode" but that is not working (progress bar but still hangs on gray startup screen). Then, I thought about hooking the two MB Pro's together via FireWire and booting the new one up in target disk mode. I was able to access the files this way, but obviously I couldn't change anything via the system prefs of the new MB Pro while in target disk mode. The only thing I could possibly think of was to change the user name on the home folder back to "macuser" in case the computer was looking for that. To be safe I even duplicated that folder and renamed the duplicate with the personal name I had first switched in the system prefs pane (causing this mess). I figured if it had two duplicate user folders, one with each name, I could cover my bases. It would recognize one at least, whichever it was looking for: the original I changed sloppily and/or the new one that I replaced it with and was now registered in system prefs. But unfortunately, that still didn't work.
I was supposed to deliver it and set her up this weekend, but the DVD copies the seller made upon my request were sent out yesterday and probably won't be here until next week. I even thought of logging in as "sudo" or root user, but everything I've read about that seems to indicate you must first set some parameters on the computer to do that before restarting, which of course I cannot access it to do. I'm in quite a pinch, so any ideas I have not thought of would be greatly appreciated, thanks!

Answer 1

Apparently the seller gets these wholesale in bulk (maybe at a discount since they are not brand new but still under original warranty and show that they are only a few months old). He said "they didn't send him any this time", but yeah, At the very least I should've gotten those DVD's with it. Maybe I'll ask him or look into securing the originals from Apple.
So is there nothing I can do until I get the discs?