If your kernel auto detects the IDE bus speed incorrectly, you can change this in lilo.
/etc/lilo.conf:
To change the IDE bus speed, add:
append="idebus=66"
either in the general section for all kernels or in the section for only a specific kernel.
Also, notes about hard disk tuning can be found at:
http://www.linuxnetmag.com/en/issue7/printm7hdparm1.html