Ringo,
You can download V4 of Turbocnc (
www.dakeng.com ) along with documentation and use it. It is not crippled in any way and when you register ($60), you also get the source code. "Hotfixes" aka "bug fixes" can be downloaded form the TurboCNC group over at ya hoo:}).
I beleive the initial download still has a sampling of g-codes in it to give you an idea of how it works.
This program works in DOS (Not a dos box in windows) so you need to boot up your machine in basic bare dos to run it.
Bubba