Winforms + webservice certificate authentication

[nano2k]

I have the following scenario.
1. A webservice (built using VSNET 2005 - .NET 2.0)
2. A winforms application that will be deployed to several
workstations.
3. Each accepted user has a security smart card (etoken).
4. The entire client/server system is not public, but accessible to
just a few users that are all connected through a VPN network.

I need to:
1. First, when a user starts the winforms application, a login form
appears. The user will enter the login name and hits the Login button.
The client app should force the user to enter the password associated
with the smart card. The smart card has its own authentication form
that should popup. This is the first part i'm stuck. How should I
invoke the authentication process from the smart card?
2. Consequently, when the user starts using the application, the
credentials should be automatically transmitted to the webservice
(how?) and the webservice should authenticate each request based on
the credentials sent by the client application.

Of course, the USB token should be present all the time while the
users is working.

Any help is greatly appreciated.
Thanks.