How do I choose between DTD or Schema?

[admin]

I'm learning how to use XML and XSLT for my masters research project : involves creating computer based notes which can be re-formatted by the student to suit their learning style.

I need to know more about DTD's and Schemas.

I get the sense that DTD's are not being used as much anymore - is this true?

It seems that some browsers cant deal with DTD's - like Mozilla and Safari. Or am I wrong about that?

But then, is it possible to define entities in a Schema like one can in a DTD?

How do I choose what kind of Schema to use?

Are there any other drawbacks/advantages to using DTD as opposed to Schemas, and anything else I should know?

Thanks!