Exactly. Lets say your encryption key is something along the lines of 1A2B3C4D5E6F7G, you'd enter it as 0x1A2B3C4D5E6F7G.

Just be warned that WEP is extremely easy for someone to crack, living in an apartment complex I'm wondering if perhaps picking up an ethernet card and just connecting the PowerBook via ethernet would be a better idea. That way you could go back to using WPA/WPA2 encryption for your WiFi.