WS-TRUST profiles and Cardspace
Geneva framework supports today the two WS-Trust profiles, Active and Passive.
The active profile deals specially with applications that are able to make soap request to any WS-Trust endpoint. On other hand, the passive profile is for clients that are unable to emit proper SOAP (a web browser for instance) and therefore receive the name of "passive requestors". This last one involves browser-based communication with several http redirects between the different parties (client, STS and relying party).
Cardspace embedded in a web browser page however is not a Passive client. Once the user decides to be authenticated in a website with an information card, the Cardspace identity selector will negotiate and get the issue token from the identity provider using the active profile. Finally, the identity provider will pass the token to the browser using some Inter-Process communication, and the browser can later submit the token to the server using an standard http mechanism like a web post.
As you can see, Carspace in a browser is actually an hybrid between Active and Passive. Vittorio has also discussed this scenario in the past, he called it "Passive-Aggressive".