Ok, the setup page will only create the admin user if it creates the site so if you can delete all the rows in all the tables it can start again.
If you can access query anaylzer then
Exec mp_Sites_Delete 1
shoud do it assuming the site id is 1
Then visit the /Setup/Default.aspx page again and it should create the site and the user but there will still be a problem.
You'll need to look in the mp_Sites table and see the new id, probably 2
Now rename the /Data/Sites/1 folder to Data/Sites/2 or create a new one and copy the contents from the 1.
Now type a space in web.config and save and upload again, this is just to recycle the app.
If all goes well it should fix the problem, though I don't understand what happened before to get things messed up. I mean it should have created the admin when it created the site, thats what it does when I test it.
Hope it helps,
Joe