Im checking all of my xml documents against a regular DTD, but ive been finding out more about Schema.
For what I do, all that i need is something simple and not have to get too in depth with requirements, so I chose to use DTD. I then saw the rough draft for Schema 2.0 (aka DSD 2.0), and it looks like it might be nice to switch over to. Which is worth checking simple xml documents: DTD or Schema?
Just call me Crash...
"Crash- and BURN!"
I'd say start with a DTD schema, then after you've got that, start developing your XML Schema document. The DTD I typically use to define the basics of the language first. Schema gets much more complicated, as jkd pointed out, but sometimes it helps to have the basic framework figured out.