hey guys, i'm taking CCNA 2 in college, and i'll tell you right now that you REALLY have to pay attention. there is just so much stuff. for me, the somewhat tricky part is VLSM (subnetting), but with practice one could do it in their sleep. the best way to study would be definitely from a paper book, however i study from Networking Academy on my computer, and it's somewhat tricky (can't highlight my monitor, can i?)
for CCNA 1 - pay attention to the OSI model, and VLSM, network cabling, router commands, they are pretty much the key points, but do read everything.
CCNA 2 - pay attention router commands (not a reprint), EIGRP and OSPF protocols, as they are more used now, you will learn about RIP and RIPv2, but thats just to give you an idea how protocols work, once you know RIP, you can forget about it.
Finally, as my professor says, packet tracer sucks, its...ok, but its not the real thing. NDG has a very nice product that my school uses, i can access real routers from home / school, as long as a i book a time slot, the only virtual aspect of it are the computers, they are vmware images, check it out - http://www.netdevgroup.com/products/ae/. And now off to school to study for CCNA 2 final exam