permission for derivative work

Hello,

I am working on a web layer to the Ruby programming language:

     http://www.ruby-web.org/

The steps of installing ruby-web are similar to the steps of  
installing PHP.  I have always admired PHP's excellent installation  
documentation, and I was hoping to adapt the PHP installation docs to  
describe the steps for ruby-web, and include them in the ruby-web  
manual.

I believe this will qualify as a "substantial modification", and thus  
I am writing to ask permission.

Please let me know if I am allowed to make this modification, and  
what notices / etc. I need to attach to the manual.

Cheers,

Patrick May