I would suggest if you can go for WPA2 and Wireless-N. Wireless N has improved Wireless Protection and WPA2 is the most secure you can get using Wireless (as far as I know).
People shouldn't be able to hack in anyways because if your wireless your Gateway encrypts everything received and sent to your computer so unless someone was sitting in front of your house and knew your wireless key (pretty hard to hack even if your using WEP).
Even as such you should have a firewall anyways because no adays no one is safe without a Software Firewall or a Hardware Firewall (not just saying your router does, that doesn't count, it only counts if it says Firewall on it).
Also like someone else mentioned earlier it would be a good idea to disable broadcasting of your SSID if possible then just setup windows to connect and specify the SSID, you really don't need broadcasting.
Hope this helps