apache offers index.php for download instead of running it ?

HI.
An odd fault has devoloped and I'm not sure what I've done or what was changed to caused this.

When I browse to my gallery2 site -
www.avtsuk.com/gallery2 explorer now offers me a download which is the index.php file, if I browse directly to www.avtsuk.com/gallery2/main.php then all is well.
If I browse to www.avtsuk.com/gallery2/index.php then again explorer offers me the download.

I'm assuming its something in php.ini or more likely httpd.conf for apache, But I'm dammed if I can find what is causing this.

Anyone had this or give me a direction to go in?

Feel free to try the URL's above and see what I mean.

Gallery version (not just "2"):2.2.4
PHP version (e.g. 5.1.6): 5.2.6
PHPInfo Link (see FAQ):
Webserver (e.g. Apache 1.3.33): Apache 2.2.4 (Unix)
Database (e.g. MySql 5.0.32): Mysql 5.0.37
Activated toolkits (e.g. NetPbm, GD): ImageMagik,NetPbm,GD
Operating system (e.g. Linux): Slackware Linux 2.6.21.5
Browser (e.g. Firefox 2.0): (Via Windows) Explorer 6.0.2900.2180 (SP2)

HI.

Now I'm confused, did all of the URL's work ?

If they do then it points to something that has changed on my desktop computer, I'm down to a single computer at home at the moment so don't have another to try from.

Grrrr..