I would suggest if you have an old PC with a parrallel port to just have a go at setting linuxcnc up with a parrallel port.
I don't normally recommend the use of the parrallel port, but if you just want to get some motion first (all you need to do is wired up the stepper motors and stepper motor drives to 6 output pins of the break out board (step + direction for each stepper) and you can get some motion.
most people would use pins 2,3,4,5,6 and 7 for the 3 x axis.
once you get some motion you can then add to it with a mushroom emergency stop (I would highly recommend if you are new to cnc as you'll get it wrong and need a quick "off" button).
and then limit switches and a probe / touch off input.
I have never used the parallel port with cnc (that includes Mach3/Mach4 + linuxcnc), but I believe you will need to install the RTAI kernel.
I don't know how much you know about linuxcnc but I'd suggest just installing from the iso here from a usb memory stick.
Don't worry about upgrading or doing anything out of the ordinary until you get motion and you get used to linuxcnc working.
LinuxCNC 2.8.0 Debian 7 Wheezy RTAI
www.linuxcnc.org/iso/linuxcnc-2.7.14-wheezy.iso
set it up with axis first, you can always change it later to something else.
choose the path most trodden and then people can help if you get stuck + its easier to learn and teach.
Once you get the iso installed, start here:
linuxcnc.org/docs/2.7/html/install/latency-test.html
basically you need to go into the PC bios (use F2 / delete / F10 at boot time) and change all the power saving settings to be turned off (any virtualisation / C states or anything that is a performance booster). You need the PC to operate continiously and without performance blips as you are looking for regular timing.
You will need to reboot and rerun the latency test a few times to see if things have improved or got worse.
You are also likley to benefit from possibly adding some improvements to grub (the GRand Unified Bootloader), but it depends if your old pc has multiple processors or cores
this is an old wit from the wiki. it's sort of relevant, even more so if you are running an older PC and older distribution. it sort of provides a bit of a guide as to what you can try to do.
wiki.linuxcnc.org/cgi-bin/wiki.pl?The_Is..._Parameter_And_GRUB2
[I use isocpus on my linuxcnc fanless 4 core pc, and it does provide improvements to my setup, but I'm not using the parallel port and have some scope / timing and latency is less important to my setup]
Once you have got linuxcnc latency looking ok / within the recommended ranges, then have a look at moving to this section:
linuxcnc.org/docs/2.7/html/config/stepconf.html
good luck and let us know how you get on.