Agreed. There is nothing better than putting your hands on the product.
In terms of reading, a few places I'd point you to:
1) Product documentation. Believe it or not, the help files are getting very
good.
2) Online you'll find the 2003 deployment kit. Read it, it has a lot of good
stuff.
3) Read the 2000 Branch Office Deployment Guide, and when it comes out read
the 2003 BODG as well.
4) White papers, such as core AD papers and things like group policy are a
great place to start as well.
Of course, just breaking your test lab is the best way! Set things up, try
and do things you think you might want to do if you were doing it for real
and figure out how to get things working.
Hope this helps!
~Eric