Getting IIS and PHP to play nicely together

Hi...I'm trying to help someone get some php pages to work on IIS, and for some reason it is not working. What happens is the index.php page has an if/then statement that redirects to the main.php page. When the user goes to the index.php it redirects fine so it seems to be doing its php thing (we can also get phpinfo to work), but the second page, main.php is blank. I'm able to get this php script working on Apache on a different machine, but for some reason it's not showing the second page in IIS.

PHP is installed, and seems to be working, but as I was not the one to install IIS and php, I suspect there's some setting that's incorrect somewhere.

Unfortunately I don't have version numbers at the moment (trying to get those) but I was wondering if anyone could give me a rough direction I should go in when trying to figure this out...I'm a total noob at IIS and I don't have an IIS system right here I can fiddle with...what areas should be double-checked? What might cause php to sorta work, but also cause a blank page?

Thank you for any hints.

If you get phpinfo() then your problem is probably in the code for the 2nd page, not in any IIS configuration.