|| Can I switch to Mysql if I previously ran my directory without Mysql?
|| Yes, you can switch to Mysql at any time.
If you don't have setup.cgi present in your admin directory where the admin .cgi script files resides, download the latest version from http://www.focalmedia.net/tbdowload.html - Then copy setup.cgi from the .zip archive to your admin directory and assign permissions of 755 to it.
Load setup.cgi in your web browser and go through the steps until you are able to supply your MySQL details. Fill in your MySQL details.
After this follow step 2 of the installation instructions. The installation instructions can be found here:
Rebuild your indexes.