http://www.theorbo.com/Theorbo/Composing.htm Lynda Sayce's page on composing for the theorbo.
http://www.vanedwards.co.uk/spencer/html/ Page images of Robert Spencer's definitive article Chitarrone, theorbo and Archlute, 15 pages in all and each under 150K
The lute in Britain online extract at Google books, needs broadband
http://www.mail-archive.com/baroque-lute@cs.dartmouth.edu/msg00347.html D minor theorbo tuning