Can't make a WEP connection work

I couldn't figure this out on my own... so I was hoping I could find some help here. What I have is:

- Desktop PC with no wireless card
- Cable internet with a "regular" Motorola cable modem (non-wireless)
- Lynksys WRT54G 802.11g wireless (& wired) router/access point
- Dell Inspiron 6000d w/Intel 2200 (b,g)

What I need is:
- Share my Internet connection that currently goes to the desktop with my laptop _securely_.

The Linksys router has a nice and friendly utility that creates a wireless network once you install the router and run the utility. I had no problems creating and using an unsecured network on both PC and laptop (PC is hooked up by wire going from router to cable modem, and laptop is using wi-fi).

However, when I tried creating a _secured_ network (WEP), I failed to connect to it from the laptop. The PC works OK (sure enough, because it's wired). I used 128-bit encryption and put the network key that was generated on PC (when running the Linksys utility) into the laptop's wireless connections settings. When I try to connect, it either tries for ~30 seconds and doesn't connect at all, or connects and says the network has "limited or no connectivity." The PC is accepting incoming connections and sharing its internet connection.

So why do I have no problems with unsecured network, yet can't get it to work in secured mode?

Thanks!