Cygwin is a great tool for UNIX people stuck in a Windows world as it provides a vast assortment of UNIX tools in a Windows command prompt. One of the most powerful uses of Cygwin is as an X server. While it may be useful occasionally to run a single X application in its own window, that can be boring. As a more exciting option, it is simple (one command) to launch a full Solaris desktop session complete with login screen.
Solaris is already set up to allow remote X logins, so you have no work there. On your Windows box, install Cygwin (if you have not already), and open a Cygwin prompt. Then type the following:
You should see the login screen of the Sun host (as long as it is on the same subnet).