With Windows 7 supporting multi-touch gestures and devices you can now make your own FTIR, DI or even a simple webcam based system to communicate directly with Windows 7. Thus, making your complete OS work with multi-touch.
Community Core Vision (formerly known as tbeta) is program which gets feed from your camera and applies filters for blob tracking. This way you can actually make very cheap multi-touch interfaces, you can find a simple tutorial for that here. After that it sends the fingers or touch data using the TUIO protocol. Now all we need is a driver to convert those TUIO multi-touch signals into Windows 7 multi-touch messages. Here is a video of CCV demo and a link to the tutorial on how to set it up.
After this is done follow the tutorial which uses another project called Multi-touch Vista. This project requires you to have Microsoft Visual Studio 2008. You can follow this tutorial and install the Windows 7 driver for Multi-touch Vista. If you follow the tutorial correctly you will be able to run your Multi-touch hardware on Windows 7 with all the gesture recognition done by the OS. You can try XPS Viewer, Photo Preview, Onscreen Keyboard and other applications to see the multi-touch in action (in other words you won’t have to use keyboard or a mouse to work on your computer). But again you need to have hardware for that. Here is a video taken by me demonstrating the multi-touch features of Windows 7.