Debating switching to linuxcnc

So I recently picked up a Carvey that had been rewired to use Grbl on an arduino uno and a protoneer cnc shield. I may just keep it as is but I am debating switching to linuxcnc as I know its more powerful .... I'm just not sure I could take much advantage of that power.

So what would be the cheapest setup to get it working. Fairly sure I can get a free C2D or P4 machine from work if it will work for linuxcnc. They should still have a parallel port on them if I go that route.

As for stepper drivers I might be able to use the cncshield as it has separate power for the steppers but otherwise pulls all its signals as 5V signals from the arduino. If I did not go this route what would be the best cheap way to go? It would need to either accept the pololu style drivers I have already or have its own drivers.

I also plan to get this board to control the spindle speed. It is controlled by a 1k-10k frequency. (Getting it either way as I currently only have on or off but figured I would mention it if it mattered.)

I have kinda used linuxcnc before but only really setup a plasma cutter with it. So still solidly in the novice stage. And this one is for me not for work so is cheap china components the entire way. (Not sure I will ever make money off it but that is the dream.)