strange installation problem

I’ve been trying to crack this for the past few nights…
I’m trying to set up WordPress on localhost on OS X 10.3.
I’ve created a database using MAMP and I’ve created a user with the appropriate priveleges. But when I go to install WordPress the instal.php file loads up saying I’ve already installed WordPress and that I should go ahead and log in. I hit the log in link and all it does is open up the window in the Finder where the wp-login.php file is held. It’s driving me crazy. I can’t open the login file in Safari or Explorer.
I’ve checked the WordPress database through phpMyAdmin and it says there are NO tables created. I’m stumped.
Any help much appreciated…