No. Windows is a preemptive multitasking enviroment. Your program can be preempted at anytime. Intensive Hard Drive accesses - reads and writes - can cause your program to be held off the processor for 10's of milliseconds. Realtime control, like motion control is always done with dedicated boards.. That being said, I've run steppers with good accuracy off of the parallel port. If your needs aren't critical, port control with Windows may suffice, but if you need microsecond accuracy, you need dedicated hardware.