Circular interpolation G2/3 implementation.

I am a new member to the group, and this is my first message, so please bear
with me.

I have just started a milling machine conversion
(http://home.freeuk.com/jaguar/milling/). However I have changed the design
as the original had some very severe short comings in terms of speed and
accuracy.

I have now obtained some constant current bridge driver
(http://www.compumotor.com/manuals/OEM/OEM350-650.pdf) They interface at
rs-232 with the PC and the 650X version can be daisy chained I believe. The
software driver has to generate X-ware a Compumotor/Parker proprietary
command language. These drivers are quite sophisticated giving you feedback
if they have stalled or not also they can be triggered so latency in the PC
operating system is no longer an issue. However the down side is no
shareware or freeware software appears to be available to drive them. I am
experimenting with NI Lab Windows, theoretically I know I can take a G-code
file and parse it to drive the Compumotors via a bit of home grown code and
panel control. I have done this sort of thing before, but it is not easy,
but it is cheaper than buying a purpose designed controller. This approach
requires me to write a circular interpretation algorithm for G2/3. There are
plenty of software applications that can produce G-code from a dfx files so
that is why I am going that route. Has anybody in the group dabbled with
circular interpolation algorithms in C (or any other language). Any other
comments on my hair brained project will be gratefully received particularly
if there is an easier route to my chosen solution.