Well, there is good news and there is bad news. The good news is that a UDMA interface can be used with both UDMA hard drives and legacy EIDE hard drives, and will be a lot faster than an EIDE interface.
The bad news is that the old stock kernels (2.0.x) do not currently support UDMA very well. The new 2.2.x kernels do support UDMA33, however, and kernel patches are available to add UDMA support for kernels that lack it.
In addition, certain UDMA interfaces that are add-in cards rather than built into the motherboard require either a patch or some trickery to use on older kernels. That is why this document exists - to explain how to get the patches and work the trickery.