1. Google! There are loads of tuts on cracking wep/wpa, etc...
2. Get Linux!
3. If you are adamant about using windows for this then you need to download the Aircrack-ng suite of tools. They have a Windows version. The problem is that you don't get any packet injection capabilities on windows regardless of the card, so gathering enough packets (IVs) is going to take some time on a quiet link. If you want to be able to inject packets on windows your easiest option is to get the airpcap usb adapter from CACE and use it with the airpcap version of Aircrack-ng.
Also, while I know that the Linux version has integrated the new PTW attack, I'm not sure about the Windows version. I would assume so. This is a FAST way to crack WEP but currently it only works with ARP request/response packets. Easy to generate with aireplay (part of the suite) on linux.
So assuming you have enough weak IVs collected the cmdline string is :
aircrack -q -n (key length) -b (bssid) capture.cap
once you have cracked the key you can either use wireshark and insert the key to read the decrypted packets or use airdecap to decrypt them.
If you only have a windows box at home I would suggest getting a copy of BackTrack. It has all the tools you need. Just boot into it.
Also, check the Aircrack-ng site to make sure your card is compatible. it really should not be a problem though. Also, they have some sample packet dumps for testing.
Oh, and the other posts are correct. It is now illegal to use another persons bandwidth (wireless or otherwise) without permission. Whether or not you'll get caught is another question.
BTW, this post is pretty much a copy/paste of the one I posted on LSO about the same topic. So google!