Umm yah, if it won't let you login then I'm kinda lost..., try going "sudo su" (sudo means run command as switched user and su means switch user to root by default), though if you can't login that probly won't work.
If you can boot into single user mode, there may be help, this is of the top of my head but it should work.
1) Reboot and hold down 'Apple+S' (will boot into single user mode as root, terminal based)
2) type '/sbin/fsck -y' (this checks your filesystem and the -y means say yes to all queries, so it'll fiix problems automatically)
3) type '/sbin/mount -wu /' (This wil remount your drive read/writable)
4) type '/sbin/SystemStarter' (this starts system services so you can access the password database)
5) type 'passwd root' (this will ask you to enter a new root password twice)
Tricky part (i hope this works)
6) type 'nicl localhost /Users/jlutz/ passwd "****" (this will tell netinfo (the mac os x user database thingy) to add a user jlutz with password ****)
7) type 'cp -R /System/Library/User\ Template/English.lproj /Users/jlutz' (this will copy the system template for users to your new home directory)
8) type 'chown -R jlutz /Users/jlutz' (this will make it so the new user jlutz now owns that directory)
and then reboot and try logging in. Sorry bout not being able to help anymore, i got a driving test, should be back in like 3 hrs.
