From Microsoft

Assistive Technology

Products compatible with Microsoft® Windows® operating systems, made by independent assistive technology manufacturers, are included in the assistive technology catalog. People who have dexterity difficulties and impairments may be interested in the following assistive technology:

• Speech recognition systems, also called voice recognition programs, allow people to give commands and enter data using their voices rather than a mouse or keyboard.
• On-screen keyboard programs provide an image of a standard or modified keyboard on the computer screen. The user selects the keys with a mouse, touch screen, trackball, joystick, switch, or electronic pointing device.
• Keyboard filters include typing aids, such as word prediction utilities and add-on spelling checkers. These products reduce the required number of keystrokes. Keyboard filters enable users to quickly access the letters they need and to avoid inadvertently selecting keys they don't want.
• Touch screens are devices placed on the computer monitor (or built into it) that allow direct selection or activation of the computer by touching the screen.
• Alternative input devices (including alternative keyboards, electronic pointing devices, sip-and-puff systems, wands and sticks, joysticks and trackballs) allow individuals to control their computers through means other than a standard keyboard or pointing device.

Adjusting Computers for Dexterity Needs

The following tutorials explain options helpful for individuals with dexterity difficulties and impairments.

http://www.microsoft.com/enable/guides/dexterity.aspx#step3