You don't really want to just randomly set options to your hard drive (DMA). Make sure you know what your drive can support first.
DMA is not usually off by default in Slack 9.1. That was an issue with 9 and kernel 2.4.20. To find out how your drive is set, use hdparm -v /dev/hda
root@dabasement:/home/scruff# hdparm -v /dev/hda
multcount = 16 (on)
IO_support = 1 (32-bit)
unmaskirq = 1 (on)
using_dma = 1 (on)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 19929/255/63, sectors = 320173056, start = 0
There is a good tutorial here
hdparm -i /dev/hda should give you some basic info on your drive.