hmm ... seems you already had run the installer, and tried again? (perhaps had some error while trying the first time?)
if so, you can check what rows that has been added with a tool like phpMyAdmin or similar, and remove those (for a complete listing of rows that's added to the config table, check the documentation chapter 2.2), and delete the files in the cache folder on the forum (so that new ones will be generated)
for the next version I might do so that old values are overwritten, but I'm not 100% sure I will (as sometimes people leave install_mod.php in the folder)
but remember to make backups!