SOAP is platform and language independent, it means that you can have a server written in any language (Perl in this case) that talks to any client written in any other language by using XML messages.

So you only need to write a SOAP client in C#, make it point to your Perl server, call any method exported and it will work.

You have several samples in the SOAP::Lite documentation, including links to WSDL files.

Update: Maybe you find this tutorial from the mono project helpuful.