First I would download the live cd from http://www.linuxcnc.org/content/view/21/4/lang,en/
and run the latency test on it.
to even see if your portable will work.. Newer portables, well portables in general, have issues with realtime.
A usb to parrallel conveter will not work..
You might be able to get a pcmcia card (pccard) to parallel converter although I don't know 100% if that would work.
Yes - gcode made in windows will work in linux. (you may have to edit the post to work with the emc2's ngc format. It is similar to fanuc)