Can't get wireless card to connect to router

Hi. I've got a 2wire SBC DSL modem/wireless router in my study, and a
windows 98 SE desktop across the house. I can't get my new wireless card
(linksys WMP54G) in the desktop to connect to the router.

Now here's the weird part: I have a laptop with a linksys WPC54G card, and
it connects to the router just fine, so it's not a problem with the router,
and I have another router in my room (Linksys WRT54G), which my desktop (the
one with the new Linksys WMP54G) connects to effortlessly, so it's not a
problem with the wireless card.

Whenever I go to the WMP54G's Wireless Network Monitor and press "connect"
on the linksys router's SSID it immediately confirms that I'm connected, but
when I go to the 2wire's SSID and enter the WEP key (which I'm positive I
have right) and press "connect," it just sits there forever and refuses to
connect.

How is it possible for a computer to connect to one router, but not the
other???