Router Questions

So basicly i had the wrt54gs router and now i bought the WRT310N

so basicly first question

I installed it and the other computer are detecting and is asking for the WEP key.. i put it in and it works fine. But basicly it keeps asking me for the key after i restart it or sometimes just randomly.. how do i make it so that i permantly knows the key??

and the other computer connects but for some reason when i open the browser it says it cannot find the webpage.

so leads me to my second question , can i use my old WRT54GS router as some sort of repeater even if the router im using is N and that one is G?