terminal services and criptoapi

I have an aplication in a data center.
My client use the aplication in a terminal services aplication from your
WindowsXP (my aplication is client/server) my question is:
How can i use an certificate (to sign an file) in my client server
aplication, the certificate is installed in a WindowsXP machine of my
client
and the application is executing in a terminal services session.
How can i access the "WindowsXP host" files, registry, activex from an
teminal services session?

thanks for help
luis