development to ISP migration headache

Hi folks, I have a site on my laptop, works fine. When I tar it up and move to my ISP for a production environment, certain things stop working. The two environments are pretty much the same, except my laptop is php_mod and the ISP is a cgi. Basic pages still work fine, but I'm using URL parsing to get variables and build pages on the fly. When I try to call one of these pages, e.g. http://hostname/page.php/foo/bar I get an "Internal Server Error" (bla bla bla internal error or misconfurguration bla bla bla) Any idea how to troubleshoot what is going on here? tia, suri