There are many paths to being a NP. First of all, are you already a RN? What, if any degree do you already have?
To be a NP, you currently need a MSN (someone correct me if I am wrong and there are still some states where you can practice without a MSN??)
However, this may change in the coming years, because the AACN has recommended that the entry degree for new NP's be a Doctorate of Nursing Practice, starting in 2015, although each state will have to decide if that is going to be "required".
Anyway, not all MSN degrees prepare you to be a NP. There are MSN programs geared towards nurse educators, nurse administrators, "nurse leaders" etc. If you know you want to be a NP, it makes sense to attend a MSN program that prepares you to sit for NP boards. However, if you end up doing some other type of MSN, you can still become a NP by taking additional coursework/clinicals in a post-MSN certificate program that some schools
Here are the options I know of:
1) The most "traditional" path is typically for RN's with a BSN to apply to MSN programs.
2) If you are a RN with an Associates degree, there are some RN-MSN "bridge" programs out there that you can enter without first having your BSN.
3) If you are not a RN, but have a BA or BS in a non-nursing field, there are "direct-entry" MSN programs that are typically ~ 3 yrs. These typically require some pre-requisites (like Anatomy & Physiology, Microbiology etc) and most do not grant a BSN along the way. You can typically take the RN boards (NCLEX) and start working as a RN after the first year or so, but you do not get a degree until you finish the entire program and get your MSN. At that point you can sit for the NP boards and start work as a NP.
4) There are also accelerated BSN programs for people with previous non-nursing degrees if you think you want to get your BSN first, work a little while, and then pursue your MSN.
Sorry I can't tell you yet what exactly NP programs are like, I don't start mine until this fall. In general, it seems like the first year is usually coursework (adv. pathophy, pharm, health assessment, etc) and the subsequent years involve 1:1 precepted clinicals along with coursework.
Hope that helps, and good luck!