PHP 5 and x-application-httpd issues

[escalf]

My co-admin decided to attempt to install a new help desk and ticketting system onto our production server, last night. A software called vTiger, that promptly did a forced upgrade of PHP, and completely hosed MySQL. He has since been chagrined into never doing an install of an unfamiliar software (particularly by a .bin installer) onto a production server, again.

Unfortunately, after spending hours fixing MySQL (and I'm still not positive it's fixed); I'm left with the wonderful x-application-httpd error, where browsers attempt to download the .php file, instead of letting it be server parsed, and display the results.

I'm currently on PHP 5.1.2. Does PHP 5.2 fix this issue, and if not, is there any way to fix it besides downgrading to PHP 4.x?

Thanks.
-Eric