How do I copy the security key?

Question

Hi - I have a 7230-4 Belkin - one machine (running XP) is hardwired to the router. The other machine (Dell laptop running XP) is wireless. I have a new HP w/Vista that I'm trying to hookup but it wants the security key/passphrase. I don't remember what it was and I'm concerned about changing anything on the router because I don't want to effect the Dell that is working. So what I think I want to do is copy the 'security key/passphrase' from the Dell to the HP but 1. I don't know where that is kept on the Dell and 2 what would I have to do on the Vista machine. One last note on Vista it asks for the key and has link below if you have the key on a usb drive. Thanks in advance!!!