Putty, it seems, is the most popular Telnet/SSH client for MS Windows (although it does run UNIX too). It is small, free, stable, and flexible. It has all the functionality one will ever need (with a few exceptions, of course).
Secure Shell (SSH) provides for a number of interesting uses. One of them is port forwarding, also known as tunneling. It is used when there is a need to pass encrypted information between two hosts while the original protocol for information does not support encryption, or another encryption level is required for some reason.
Apparently, Putty can help poor Windows souls with port forwarding too. This step-by-step tutorial with a lot of pictures shows exactly how to do it. The example used is encrypted email traffic.