Free, open source (kinda) viewer that lets you remote view your computers over a LAN or Internet (although with some tweaking to your firewall and consequent security implications).

This software is great for remote admin of a box but WILL NOT give you the framerate you need to play games on. Not even close. You can try it but no matter how fast your network, it is just not going to happen. The future will likely be virtualization and being able to use 3d acceleration to run multiple entire OSes at once with full 3d acceleration for each virtual "OS". As for VNC, it serves its purpose and is great software but is NOT designed for gaming.

From the VNC website:

"VNC stands for Virtual Network Computing. It is remote control software which allows you to view and fully interact with one computer desktop (the "VNC server") using a simple program (the "VNC viewer") on another computer desktop anywhere on the Internet. The two computers don't even have to be the same type, so for example you can use VNC to view a Windows Vista desktop at the office on a Linux or Mac computer at home. For ultimate simplicity, there is even a Java viewer, so that any desktop can be controlled remotely from within a browser without having to install software.

VNC is in widespread active use by millions throughout industry, academia and privately. There are several versions to choose from, including a free version and some substantially enhanced commercial versions."

Also be aware that there are several other VNC versions out there - some of which may work better for your application. Nearly all of them are cross platform, allowing you to control different types of OS (like XP) from other kinds (like Linux).