Perfectly reasonable question.
Denford will still sell you a license for their software (about £250 IIRC), however the older RS232 only machines will only work with version 2 of their VR software, which has various limitations. But it still leaves the issue that RS232 is not much use if you're doing 3d work, as you run a high risk of buffering issues with not being able to get the required motion to the board quick enough.

The details for the MINT language can be found at http://www.baldormotion.com/products/mint/MINT.asp and I know Mad Professor was reverse engineering the serial protocol until he had to stop due to some personal issues.