Trouble connecting to sbg6580 router/modem

I have a wireless-g pci adapter in my old desktop and I'm trying to connect to my new motorola sbg6580 router/modem.

My wireless will pick up the router just fine. When I go to connect I'm prompted to enter security key, I have made absolute 100% sure I'm entering it correctly.

HOWEVER, every time it says "waiting for the network..." and loads for 2-3 minutes then it just closes.

I don't understand why it isn't connecting, I have an itouch and a newer laptop that connected wirelessly no problem. I also have another desktop connected directly to the router that is connected to the internet.

If I left out any crucial info please let me know. And thank you for any help

is the wireless using WEP or WPA mode?

if it is WEP have you tried both lower and upper case letters?