After entering initial installation details, I get the following error:

Unable to connect Jcow for generating the secure key.

My site is forced to run on a subdomain, which may be the cause of the problem, but this is the given PHP message:

Warning: file_get_contents [function.file-get-contents]: failed to open stream: HTTP request failed! HTTP/1.1 403 Forbidden in public_html/network/install.php on line 180

I can't change PHP settings... Please help!

jcow works perfectly on subdomain.check your php config i think u have disabled allow_url_fopen. try this free web hosts www.x10hosting.com, [url]http://www.heliohost.org/..[/url]
also you can get a free tld here www.dot.tk