Before we go further, it is worth mentioning a few other items that are similar to touch screens.
The now discontinued 3Com Audrey Web Appliance is a self-contained unit with a touch-sensitive 640x480 screen that utilizes a stylus for input. The nice thing about the Audrey is that it has built-in support for displaying and interacting with Flash 4-based content. You might be able to pick up one of these on eBay for less than $100.
There are also touch-sensitive web tablets, such as Fujitisu's Pen Tablets:
as well as Transmeta Crusoe Processor based web tablets. Most tablets capable of running a variant of the Microsoft Windows 95/98/ME/NT/2000/XP operating system should support the Flash Player plug-in. The recently announced Mira by Microsoft doesn't have too many public details about its capabilities, but you can imagine that if it's based on a version of XP, then there is a good chance that there will be a Flash Player available.
Finally, if you would like to use a touch screen during the development process for creation of Flash projects, then you can use the Wacom Cintiq. This is a 15-inch LCD that is not only touch sensitive but has 512 levels of pressure sensitivity, and can even detect the tilt of the stylus, allowing you to make unique brushstrokes. It also supports the newer DVI standard for connecting to your graphics card for better detail instead of going through a standard VGA connector. Since Flash 4, the Flash authoring environment has built-in support for taking advantage of the pressure and tilt sensitivity of Wacom devices. The Cintiq product is designed to either stand or be held for use.
See Wacom's site www.wacom.com for more information about the unique Cintiq product.