I remember having the PC with RH6.x on it, it worked sweet.
I had +,- the same problems, till I discovered the hdparm command.
type
hdparm -c1 -d1 /dev/hda
that will enable the DMA and set the 32bit on the HDD, you can test the encrease of performace by typing hdparm -tT /dev/hda
You can do this on the CDdrive aswell

....
Ginux