using web service

[kuldevbhasin]

hi
i am interacting with another package using webservice.
now the 3rd party who has developed the package has given me a link for the webservice.

http://??.??.??.??:8080/ABMPDA/services/PDA?wsdl

the above is the link to the web service. ?? being the nos.
now i have added this web service to my package.
i am developing the software on a PDA to use this webservice to get and update data to their package.

i have declared the webservice as

Dim AbmService As New WebReference.PDA

and set the url as under:

AbmService.Url = "http://??.??.??.??:8080/ABMPDA/services/PDA?wsdl"

they had send me the instructions as under:

Response of 1st isAuthenticate(java.lang.String,java.lang.String) method are-
            a. Two input parameter (Tax collector officer login name and password defined in MAInet). 
           a. If user is valid user then o/p will be:-  
                    Valid User^71        (Note- ‘^’ indicate separator, contain two parameters i.e. Valid User, 71) 
           b. If user is invalid user then o/p will be:-  
                   Invalid User

i am calling the method as :

 Dim mRetStr As String = AbmService.isAuthenticate(TxtUserName.Text, TxtPassword.Text)

it is not letting me to pass the parameter it is giving me an error
i have attached 2 images to explain how i have done.
in the first image i have just placed the dim abmservice statement down but actually it is before it.
they r saying we have explained u everthing and u need to change the way to call the webmethod.
can someone pls. guide me how i go around i am not getting any further help from there side.
pls. help me out as i have to show the demo at the earliest.