blank white screen after quickstart/php5 help

I installed the Sporter Quickstart (Joomla 1.5) but see a blank white screen on frontend and admin.
I called the web host (Web.com) and asked them what version of php is running.
They said php4 is default but the system can run php5.
Please give detailed information on how to edit the htaccess.txt file in Sporter to run php5?
Or is there a better way to fix this?
Thanks