Extra Axis feed speed

I was thinking of using linux CNC for a 3d printer im building, but one issue i havent been able to figure out is how to set the speed of the extrusion stepper, the current cgode genreated by slicers has the following format,

G1 X132.736 Y121.884 E0.9138

The E part referring to the extruder rate, I have sorted out a .net application to allow me to parse the slicer output and alter it to fit liinuxcnc, and i could change the E command to an S spindle speed command, but can i set up the spindle as a stepper axis, i was hoping at least to begin with run it on a simple parallel port breakout as ive got one kicking around, but if i need to go FPGA to accomplish it i can.

Im new to linuxcnc, although i have a Fanuc VMC and a prototrack lathe so im not new to the whole subject. Any help would be much appreciated.

Thanks

On the same subject, at the moment it looks like i need around 10Khz on the step generator is that too high for software step generator?

their certianly are versions running under Linuxcnc etc
here's one that i know of , and also take a look in the forum and the wiki here .

code.google.com/p/casainho-projects/wiki/3DPrinterEMCRepStrap

Linuxcnc has the capability of 9 axis or Joints to be more specific , depending on what connections you require 4 axis and limits etc can be fitted to a parrell port .
a mesa fpga card could be used of course .

you could use a M10x Macro for the extrusion rate i'm sure

Yeah i had a look through some gcode generated for my ultimaker(which has been in bits for a year) and it seems the extruder value is an absolute value of extruded length, the thing resets the length to 0 at the start and prints whatever the length is in each block. I had assumed it was a rate rather than a length, i guess as its a length its simply classed as another axis, making life easier!

cheers