closing a remote connection from another computer?

I'm running two laptops with XP/Pro via wireless, one is
a gateway to the internet via dial-up (A), now I know
that if I enable all the "Share Internet Connection" tags
in the advanced preferences of the dial-up connection on
(A)that the second laptop(B) when starting up will cause
(A) to make a connection to the internet, which works OK.

My problem is that I cannot figure out how to disconnect
the dial-up connection established on (A) from laptop(B)
once I have finished, even though the tag for allowing
this to happen is selected I cannot figure out what I
have to send to laptop(A) to cause it to disable the
shared connection.

Any Ideas?

Pete