I did the Essentials & IT Tech. They were much easier than I expected w/ hardly any questions on processors, IRQ's & the like.
I only used the Sybex book:
http://www.sybex.com/WileyCDA/SybexTitle/productCd-0470048301.html
Note I have no professional experience yet but I've built a few gaming PC's.
Basically, as long as you read the book (focus quite a bit on the customer service aspect of it) you'll pass the 1st time.
Seems to me that the 2003 exams are significantly more difficult.