Thanks again to Gadi for this info:
Bus mastering DMA support for the Intel TX chipset is available in 2.0.31
and above.
In older kernels (such as Slackware 3.4's 2.0.30), the controller will be used in the slower EIDE mode. In either case the controller will be automatically detected by the kernel and you should have no trouble using it.
As far as I know there is not a patch to enable full UDMA transfers, but having Bus Mastering is still better than not.