Motor controller recommendations?

[John Faith <jfaith-at-nwlink.com>]

All,
I am looking for recommendations for a motor controller.  I have a 
Sherline mill, stepper motors, and the coil driver circuits which I 
would like to connect to a newer Mac running OS X.

I have looked at the RMV ST400NT which seems ideal for controlling 4 
motors and auxiliary I/O, and it connects via serial port, but according 
to the company, they will only support Unix/Linux by shipping their 
source code, requiring that you buy several units, and requiring that 
you sign a non-disclosure agreement.

I have also seen a description of the MicroKinetics MN400 which is also 
a serial connection, and they publish their serial commands, but it 
seems like it has less I/O for a bit higher cost than the RMV.

Does anyone know of similar controllers, especially ones which which 
come with a bit of example source or at least a published interface?

Thanks in advance for any pointers,
John Faith