Ubuntu has a NetworkManager applet comparable to knetworkmanager, which is the the applet used in many KDE distros.
Are you using iwconfig to configure your wireless or some other graphical tool. The manager applets I've seen sometimes require a '0x' before the encryption key and some don't. iwconfig does not accept '0x' prefix when setting the key. If you use a gui app, you need to make sure the right encryption modes are set.
I'm pretty darn sure the chipset you have supports wep 64/128 (aka 40/104). I spent a lot of time working on the wireless when i first put linux on my laptop. I came to the conclusion that broadcom chipsets suck and my next laptop would use an intel chiipset.
-j