You wanna look into using the backtrack live cd.
I used to mess with this type of thing years ago.
Wep is simple enough to crack. Last time i checked, you only needed to collect about 10k packets.
Wpa on the other hand can take awhile. Depending on password strength.
All you really need to do is capture one packet once you're associated with the router.
You would also need to download a huge word list to brute force.
I wouldn't say its hard to do or alot of work. I mean you can get lazy and use a script someone has pre made.
I made myself an auto crack script so all i needed to do is choose the ssid from the list and it would configure my senao
card and crack the wifi.
Lots of info online about this, just read it.