Microsoft Remote Desktop with rdesktop and VNC client with vncviewer are available for OpenSolaris installation with IPS. In this funny example the first connection is a VNC connection from my OpenSolaris desktop to another OpenSolaris ESX Virtual Machine, and the second connection is a Microsoft Remote Destkop Connection from the OpenSolaris ESX Virtual Machine to a Second Microsoft XP ESX Virtual Machine.
To Install VNC client and rdesktop Client with IPS under OpenSolaris
# pkg install SUNWvncviewer
# pkg install SUNWrdesktop
To Run VNC client
# vncviewer <hostname_or_IP_address>
To Run Microsoft Remote Desktop Client
# rdesktop <hostname_or_IP_address>
To Allow Remote Desktop From Windows XP Use This Procedure from Microsoft, and To Allow VNC connection From OpenSolaris use Gnome Menu System Preference Share Desktop or you can use Xvnc which is bundled with OpenSolaris (To enable Xvnc).
Have Fun with OpenSolaris...