Tunnel from AIX machine to WinXP machine?

I've been tasked with setting up a SSH tunnel from an AIX machine to a
WinXP machine. The network is set up like this:

AIX machine
|
(PPP link)
|
Cisco router with PPP server
|
(ethernet)
|
WinXP machine

Every time the AIX machine connects to the Cisco router using PPP, I
need a SSH tunnel to be automatically set up from the AIX machine to
the WinXP machine. If all traffic could be encrypted with SSH, that
would be great; if not, encrypting single ports would be OK too (we
have a specific application that needs to communicate from the AIX
machine to the WinXP machine, and encrypting that port alone would be
sufficient).

The AIX machine has OpenSSH installed.

The WinXP machine has no SSH software that I'm aware of.

So, my questions are:

1) What software (preferably free) do I need on the WinXP machine?

2) Are there any online resources (HOWTOs, etc) that could help?

Thanks in advance.

.