Installing PHP part 2

Hi Thanks to those who have tried to help me so far, but it has been to little success. I am using PHP3 (I am unsure as to the minor version codes), and PWS on windows 98 I have followed all of the on site, and off site installation instructions for PHP3, down to moving all the PHP files to default folders. When I point to a .php, or a .php3 file, all I get is a HTTP 500 error. But when I look at a HTML file, I can see it ok. What is not working, and how can I fix it ? I am rapidly running out of time to evaluate PHP, then I will have to switch to a more 'commercial' source for my development as my customers won't wait much longer, so please help if you can, I would rather push PHP than an even more microsoft biased solution TIA Matt.