Usually, when something like that happens (initial user not setup/tables already created) one is tempted to start over ... dump the DB and TIA (try it again!). However, you might try this first ..
ssh into server as root user or sudo -s to stay root.
Change into /path/to/moodle/code/admin/cli/
Run php install.php
That really steps through the same sorts of things the web browser session does, but involves only php, the scripts, and the DB ... apache taken out of the loop.
I've had similar issues upon install using browser before and managed to pickup where I left off via command line.
Good luck! ;)
'spirit of sharing', Ken