Multi-page autocomplete / screen web form

First I apologize if this is a duplicate question, I spent some time searching and cannot find anything similar.

I need to automate the completion of a multipart web form and then process the result from the asp.net system. The ideal solution would be to create a web service that takes some data, then processes it through the website and returns the result - I can use it in any application that requires this functionality. The form that needs completion is quite complex and also includes some if / then / else logic as it goes through, like this:

• Complete personal information
• Please enter postcode
• If 1 result is found goto 5
• Display list of possible addresses when one selected goto 5
• If the time at the address is <3 years, display the new address page

and etc.

I created a solution that launches an ActiveX browser control and manipulates the website as if the user was typing in, which works well, however, it is limited to a limit for concurrent users (something> 1 starts to cause problems,> 2 is not allowed by installations by Windows default), is there a better way to do this? I have heard about Selenium, although I haven't used it, would this be a possible solution?

I have looked at using the WebClient class and have used this in poast for screen cleaning systems, however I do not know how I could combine these calls together to provide a complete workflow.

FYI - this work is carried out with the full understanding and consent of the site owner. They have a development task queue for which building the internal API does not work that way, as long as they are happy with this solution, which will not be implemented, will not be able to change anything.

Thanks in advance