I did it at university as fun thing to do, seperate to my degree. I used the online resources and the official CCNA books and probably did about 3 hours a week, plus a couple of hours more for playing around on equipment.
It helps if you get some stuff to practice on. I got a Cisco 2611 router, a Catalyst 2924XL switch, and a second router that I can't remember the model of at this time (Cisco SOHO router) for less than £250 in total. Well worth it.
If you don't wanna get equipment there's supposedly a pretty good emulator out there, but I don't know much about it.
I done the ICND1 & ICND2 courses over two weeks and swatted up using PacketTracer and the official Cisco Exam books, then finally sitting the all-in-one CCNA exam. One of the lads on the course was using a Sybex book which I had a flick through, it looked very similar to the official Cisco books although it taught you how to do subnetting a different way - not that it matters, so long as the answer is the same