A. Accessible vehicle specifications are here: http://www.access-board.gov/transit/html/vguide.htm.
Regulations are here, with the paratransit provisions beginning in section 37.121: http://www.access.gpo.gov/nara/cfr/waisidx_08/49cfr37_08.html.
The Draft Paratransit Eligibility Handbook is here: http://ntl.bts.gov/DOCS/manual.html
The ADA Paratransit Handbook can be purchased from NTIS: http://ntlsearch.bts.gov/tris/record/tris/00343582.html
And FTA's ADA homepage has a lot of useful information: http://www.fta.dot.gov/civilrights/civil_rights_2360.html (Reviewed: September 2010)