Argh, wireless router help

[Lirange]

So I went to walmart today, hoping to buy a wireless router. We ended up not buying once since we were kinda unclear on what to get and didn't have enough money. So theres 3 types of routers, highest being an n and lowerst a g. It said that the g is only good for like.. sucky stuff. Like browsing the web, checking your email, simple stuff like that. It said it couldn't even stream videos. And the N does everything, including gaming...which is a must for me. Well how accurate are these g and n things? And if i buy a wireless router i'll also need to buy a flash drive looking thingy that finds wifi for me right? Only for my desktop pc though because i believe my sister has a built in thingy in her laptop, because when we try to get a connection, we see lots of wifi, but it's secured. =[ But when she's at campus she gets their wifi. So i'll only need it on my desktop correct?
And the n one cost like, a hundred bucks!D: just for the router>.>

Btw, how safe and easy is it hacking into someones secured wifi?xD