This came up on the QIAT (quality indicators for assistive technology) listserv, and there was neat info in the answers;
http://udl.cast.org/udl/index.cfm?i=353 is a neat article about teaching disabled and non-disabled students to type (or should I say “keyboard?” - no, that’s a NOUN, I refuse!). There’s also more information and links about the question “how fast should my special needs kids have to type before they will find computer stuff useful?” which of course depends on the situation, but there are some common considerations. That’s at http://www.customtyping.com/news/ct_schools/2005-05/index.htm which has some neat free stuff like online typing tests.