I am a physically handicapped writer. I don't go with the more PC practice of calling myself "disabled" because today's technology allows me to do almost anything a non-handicapped person can, and I'm quite able to keep up. However, I realize many people find the term "handicapped" offensive, so I apologize in advance for my non-PC attitude.
For writing I use Dragon Naturally Speaking voice recognition software, which I have discussed several times on PBW. Here is my original report on how it works for me; here's a discussion about it at another site; and here is a consumer comparison chart on four of the top-selling VRS programs.
I don't belong to any writer organization or community, but recently I came across a UK-based site called Disability Writes. According to their site, it's an online community that "actively supports and encourages disabled writers, whatever their previous writing experience. Our aim is that disabled people can, through using this site, learn and develop creative writing skills in their own time and at their own pace. We promote the work of disabled writers to a wide audience of disabled and non-disabled people through this website and printed publications." I can't personally endorse the site, but it's the first I've found that is primarily for handicapped writers.
Here are some other resources you might find helpful:
Click-N-Type Virtual Keyboard
CNT keyboard customizer (to customize Click-N-Type keyboard)
Cyber Buddy text-to-speech freeware
Dot-to-Dot MacIntosh Braille Editor
EZMagnifier screen magnifier freeware
Java Accessibility Helper (aids developers in making their JFC-based programs accessible to users with disabilities.)
MouseCam screen magnifier
Natural Reader text-to-speech freeware
Philing.net's free braille and deaf language fonts
Point-N-Click virtual mouse (designed to be compatible with Click-N-Type keyboard)
Rapid Keys Intelligent Virtual Keyboard
Other resource lists elsewhere on the Internet:
Grants for Disabled Writers; Helpful Products for Blind and Physically Handicapped People; Simtel's list of 114 programs for the handicapped user; also this page of links to programs for handicapped users