Custom Dll's for php

Hi all. I have posted about this on here before but the lack of response implies either my question wasn't clear, nobody knew the answer or everybody ignored me :-) anyway, I will post again. I am a fairly good C/ C++ and php programmer. However I find that php does not have everything I need. however I have written dll's before but I understand that they are not standard dll's but they would make a good way to access api, so does anyone knowthe process for writing a dll which php can use? or a good tutorial would be equally as good. Thanks Darren