DMA for parallel port on COMPAQ ML370

I folks, I've a COMPAQ ML370 running SuSE 8.0, and the parallel port is rather slow (well, works fine, but with a 300 LPM Printronix's printer do you see the difference!). I already chanegd the IRQ from -1 to 7; but now I want to change DMA, I used both 3 and 0, but still the /proc/sys/parport/parport0/dma have -1; any ideas? Thanks, Jean H//