Aiki-ken is generally
used as a tool to improve empty-hand technique, rather than as a 'sword' art in its own right. Some variations exist.
Kenjutsu is a generic term applied to a number of sword-based martial arts that center around use of the sword as primary component of the art, but may also include pole arms, small arms, empty-hand, esoterica, religious practice, etc.
What's the diff? Sometimes not much. Sometimes world of difference. Not much of an answer, I know, but there's lots of variation in how aiki-ken is taught.
For info about kenjutsu schools, take a look at www.koryu.com
, among others. Koryu.com is an excellent site and there are, IIRC, a couple of articles there about the difference in aiki-ken and kenjutsu (from a particular individual's point of view).
I also highly recommend the Koryu Books trilogy, available from that website.
Other Japanese swrod resources include the iaido-l mailing list (http://listserv.uoguelph.ca/archives/iaido-l.html)
. EJMAS (http://ejmas.com
) is another good online resource.