Known working settings for using a static, wireless address on a Raspberry Pi running Raspbian 7 Wheezy.
interfaces goes in /etc/network/, and wpa_supplicant.conf goes in /etc/wpa_supplicant/. Raspbian should already have the wpa_supplicant package installed, but you may need to apt-get it if it's not there.
You'll also need to add in the settings for the network you're trying to connect to. It's also a good idea to back up your current settings before pasting these in.
Obviously this isn't a magic bullet, but it works for my Model B even after the Raspberry Pi 2 update that broke some other things. It's also worth noting that I'm using the Edimax EW-7811Un adapter, though it shouldn't really matter.