Have you tried passing the "ide=nodma" parameter to the kernel at bootup?
To do this manually, you can hit tab at the boot window, then manually enter the name of the kernel you want to use, then at the end, put the parameter like this:
This should start the kernel with dma turned off altogether.
If this works, you can also put it into an 'append' line in /etc/lilo.conf for the kernal images you use so you don't have to do any manual steps. (Don't forget to run lilo after editing to actually incorporate any changes made in the config file!)
See Documentation/ide.txt in the kernel source tree for more info on what you can do.