I have done lots of data acquisition and data streaming using PCs. The solution to the real-time problem is to equip the interface with a FIFO memory with sufficient depth to bridge across the periods when the PC goes to sleep. A lot of the commercial data IN/OUT cards (A-D/D-A) use this technique.
It is very difficult to do this through just a Parallel Port.
It is very difficult to do this through just a Parallel Port.