Could somebody help me install soap extension?

Dear friend,

I want to install post affiliate pro in my web site. There is one getresponse plugin intergrate with post affiliate pro. So When I hope to integrates one software with Getresponse plugin, I clicked software panel, they said I couldn’t install because “Plugin can not be activated, soap extension is not installed in your php. Please install soap extension first!” Could somebody give me hand to help me install soap extension with thanks?

Pls give me reply or write to if you would like to help with thanks.