Slow Printing thru LPT

We have problems with systems hanging while printing screen shots thru our AS/400 to the local printer. The users can’t do anything until the print job is completed. When they send the print job to the same type printer connected thru a HP jet Direct card (located in our computer room), it goes thru immediately and the user has no problem continuing on with their tasks. We are using WINNT 4.0 and W2K.