Host Sharepoint application which is using Single Sign for integration

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C#3.0

IIS7

C#

ASP.NET

IIS

, +

Hi,
I have an Asp.net application which is using Sharepoint [wss 3.0] as backend for storing the document library.Both the application[the asp.net and sharepoint] is getting authenticated with ADLDS. There are few pages developed in Sharepoint on which the user will be redirected from asp.net application. For not getting the authentication pop up from sharepoint I have used Single Sign on with form Based Authentication.
The problem is that:
1> For Sigle Sign on to work,the host header needs to be the same.[To the best of my knowledge..]
2>The client doesnt want to show the port number being used in the url.

We are stuck up at this point ,as without specifying the port number how can the default url [which is binded to asp.net application with some default port number (consider the host header part only)] will get redirected to the Sharepoint application which is hosted on some other port number [with same Host Header name (for sigle sign on to work)]?

Is there any better approach for hosting the Single Sign on application of asp.net and Sharepoint application to work on production server ?