Hiya I tried to install oscommerce manually, the first time im able to access the install page untill like step 3, the page suddenly turn into a 403 forbidden page....

Even when i reupload a fresh copy of the oscommerce files, i still get the 403 forbidden page, anyone got any idea how i can solve this problem?? im on directadmin control panel...thanks...

How to i enable the permissions to be given??

Try following these steps:
http://www.oscommerce.info/kb/osCommerce_Development/Installation_and_Upgrades/41
http://www.oscommerce.info/kb/osCommerce/Installation_and_Upgrades/225

If you still get the same errors, ask help from your web host or oscommerce forums.

Thanks for the help