Creating SOAP web service for VC++ dll

Question

I have been using a VC++ dll in a Dialog based application so far. Now, I am trying to provide the dll as a web service without re-writing or migrating the code.

I was researching on various ways to set up the web service,

1. I have setup the web service using C++ cgi in IIS. But it sounds like old way of doing things.
2. My second option is to have an asp.net script that loads the dll. I am guessing this would give me problems since my dll is not reentrant. Yet to try this.
3. SOAP and REST seems to be the jingle words for web service. Would appreciate if anyone could give me steps to create a SOAP or REST web service from VC++. I wouldn't prefer to add a C# layer since that might affect performance.

Is there any other better way to accomplish this?

Thanks in advance.