For WPA: you need to use wpa_supplicant, as the whole connection is managed with it. You will need to edit /etc/wpa_supplicant.conf to add your info and then launch wpa_supplicant to try the connection. Search the forums as there are several how tos about this matter.
For the IP address: if you want it the easy way, use the wireless assistant, which will store WEP keys, IP, DNS and gateway for every network you connect and setup. If, as it seems, you need WPA, you'll have to go for the proper way: search for info about /etc/rc.net, there are also how tos in the forums.
Suggestion: use google and try to help yourself before asking for it, as it is clear you haven't done that this time. Googling "how to wpa backtrack" gives a perfect tutorial as first link.