Something that I didn't see mentioned above was if your web server is set up right. I was trying to get a script to work a while back that wouldn't display in a browser. Come to find out that I had to tell apache that it was alright to allow scripts to run and then display to the screen. I could run it from the command line and get the output that I was looking for, but when I tried to launch it into the browser, all I got back was the script itself. I finally figured this out after asking several people about it.

If you think that this might be the case, check the Apache (or what ever web server you might be using) documentation to see how to set it right. I am not remembering off the top of my head what is needed, but remember it was a pretty simple fix when it got right down to it.