The installation is very similar to rc2 and 2a. Just follow the steps provided.
The first screen also gives a summary of whether osCommerce will work on your server:
If any of the items here has a red cross (unless they are optional), then osCommerce will not work. Contact your hosting provider!
If all looks good, then continue the install procedure. At step 3, there is now a change to allow you the shop owner to change the name of your admin section – please PLEASE change the name to something completely random.
Once the install is complete, please go to your admin area and insert your username and password, to enter. The first page that you will see after logging in is the overall summary page, which includes this message:
You must now correct these errors – do as the message says! Once properly done, the message looks like this:
Next, go to configuration > administrators. Here you will see your admin username, along with a large pink message like this:
Click the  button and type in a new password, and tick (check) the checkbox to enable .htaccess protection.
Click the [save] button. As you enabled .htaccess protection, a grey box will popup asking you for your username and password.
Insert them and press the [Log In] button. If done correctly, you will see this message:
The installation is now complete.
If you are unable to install osCommerce, please get in touch as I will be happy to help for a beer fee.