Just wanted to put this info out in case others are in the same boat. I picked up two refurbed ThinkCentre's from Tigerdirect, think they are model S50, to use as control PC's.  Switched over from deskCNC to Mach3 to try out and motors would run very rough and stuttery. I scoped out the pulses from the PC and found that the onboard port only outputs about 3.5 volts. I'm connecting directly to older 5A choppers drives and they totally don't like this low logic voltage.  

The Solution, I picked up a PCI parallel port card for $22 from the local computer store and now get a full 5volts, and motors now work great.....
Got this one http://ca.startech.com/Cards-Adapters/Parallel/Low-Profile-1-Port-EPPECP-Parallel-PCI-Card~PCI1P_LP

Also just to add, if your trying to find out how to tune the current output on the old Camtronics 5A chopper drive boards(kit), here's the details:

Connect the VOM with the black lead to ground and the red lead to the Vref test point. These are located by Q9 and Q10. They are the large pad with the heavy white outline. Set the Vref for the current that you require. The formula is Current = Vref times .1/Rsense. Since the value of Rsense is .05 ohms . The current will be Vref*.1/.05. So if you place black lead of your VOM on one of the mounting holes and the + Red lead on the test pad  and adjust R38 and R39 to the value that you want.  Thus a Vref of 2.5V on the two test point will yield a output current of 2.5X.1/.05 for 5.amps.    

thank you for your advice.  I did the same thing with the ibm thinkCentre from Tiger Direct.  Thanks again.  Cleve