Here is a general listing of the production/serial number ranges of the various BK117 models produced by MBB/Eurcocopter and Kawasaki over the years:
http://www.helionline.de/bk117.htm
Unfortunately, the links on the website don't work anymore, but nevertheless, it will give you an idea.
The BK117 A1, A3 and A4 models came equipped with Lycoming LTS-101-650 turbines, the B1 and B2 models with Lycoming LTS-101-750 turbines, and the C1 and C2 models with Turbomeca Arriel 1Es.
The B2 and C1 models both have slightly beefier (wide chord) tailrotor blades, which boost the MTOW compared to the A-3, A-4 and B-1 models (see
Eurocopter BK117 Upgrade.pdf).
The EC145, or if you will BK117 C2, essentially is a stretched and beefed up version of the BK117 C1, with a higher MTOW, revised tapered main rotor blades and an EC-135 nose and cockpit wedged onto the front of it. Eurocopter markets it worldwide as the EC145, whilst Kawasaki has the rights to market the aircraft in the Australasia region as the BK117 C2.
Incidentally, if you check the serial number/production plates of all the EC145s produced by Eurocopter in Germany, the aircraft still is certified as a BK117 C2 (despite it being called the EC145). By certifying the aircraft as a further development of the original BK117, the development costs were kept to a bare minimum and Eurocopter avoided having to go through all sorts of certfication testing associated with a brand new aircraft. Same idea as the EC130 B4 being a further development of the AS350 B3.
More information is also available under
Airliners.net.