Voice cast updated (artists added to performers and naming of the roles based on Fate/Zero anime adaptation - Bluray boxset for the first season has official English subtitles and every actor reprises the role as on these drama CDs).
Same info is for F/Z drama CDs vol. 2, 3 & 4.
Few artists aren't in the VGM database (edit - added them), but names/readings can be confirmed on these pages:
Jouji Nakata
http://osawa-inc.co.jp/infos/index/00103
Sachie Abe (she has changed the name in the meantime Sachie -> Akina, but on these CDs she's Sachie)
http://toritorioffice.com/abe_a.html
Tarusuke Shingaki
http://www.mausu.net/talent/tpdb_view.cgi?UID=108