I suggest you download this before it is no longer available:
ftp://machsupport.com/Mach/Mach2R6.11N.exe

It is demo CNC software (1000 lines of code max), current versions are now Mach 3 and 4:
http://www.machsupport.com/software/mach3/
Without a license, Mach3 will operate in Demo mode. While in Demo mode, the software has the following limitations:
•Mill & Plasma: 500 line gcode limit (10,000,000 limit after licensing)
•Turn: 50 line gcode limit (10,000,000 limit after licensing)
•Kernel Frequency locked at 25kHz (only applicable if using the parallel port driver)
•Set Next Line function disabled
•Run From Here function disabled
•Turn: Threading disabled
•Plasma: THC functions disabled
Mach software can support multiple axis, you only have to use one and ignore the others.

You will be able to move the head along your axis as you want it. You can make your own G-code scripts that will control the head.
http://en.wikipedia.org/wiki/G-code

Your requirements will be relatively simple for what the software and hardware can do. You will move along a single axis, ie: G1 500,0 moves 500 units left, G1 -500,0 moves right. Read Mach 2 help files for exact syntax.

Simply put:
- edit your G-code file.
- run Mach 2 software on PC using G-code.
- Gecko drives connect to PC using parallel cables.
- Mach 2 uses G-code file to tell the Geck drives what to do.
- the Gecko drives moves the head along the main shaft using limit switches.
- Mach 2 has manual override to move drives.

If the head has complicated movement, you can replace the Mach 2 software with your own PC interface.

Robert