Well that does help although I'm a way off yet

Ok so I get a page rquest from chillisoft like this

http://someip/hotspotlogin.aspx?res=notyet&uamip=ip-address and a bunch of stuff

I return a webpage with a username and password feild and that same querrystring at the top

they post back the login page and (this is the important bit I'm unsure on)

a) chillisoft strips out the username and pasword and goes to the radius server

b)It comes back to the IIS server I take the uasername password put them into hidden feilds having incripted the password then return the page with res now changed in the querrystring to DoLogin.

My question now is whats the name of the feilds chillispoft is looking for.

If it's a whats the name of the input feilds and for that matter what type?

If it's b whats the name of the hidden feilds got to be?

Second thought
I have to say that even reading this now it seems you are suggesting a third method where the returned page includes a link like this http://router-ip/login?username=user&password=encryptedpassword and thats what send chillisoft off to the radius server to authenticate.  In which case do I even do anything with the res var?  Or store anything in hidden varibles?

Clearly I'm still confused