I have a laptop that has Mobile broadband.
I can only use the Mobile Broadband card on that laptop.

Is it possible to connect another computer to that laptop via an ethernet cable or any other cable to use that internet connection?

It can be done. You will need a crossover cable to connect between the broadband card of your laptop with the network card of whatever computer you need to connect to the internet with. You then need to enable internet sharing from the Advanced tab of the Properties of the connection from Network Connections.

don't you rather mean a crossover between the ethernet card/port of both computers?

i hope thats what he means.

thanks!
I'll let you guys know how it works.

yeah, that's what I meant.

it didnt work. do i need to have the same OS on both computers?

No it's not necessary. Can you give more details about your comps (OSes mainly)

do you mean MAC/Windows or do you mean versions of windows.
in the first case, maybe, I don't do Mac.
in the second, no but you might have more to do if Vista is involved maybe.

yup.
I have the internet connection on XP laptop and I'm trying to connect a Vista laptop.

oh, the humanity.

Does your laptop have XP Pro on it, if not, you will have difficulties sharing your internet connection.$*
If it has XP Pro, then, connect your 2 PCs with the crossover cable and on your laptop, go to control panel-->network connection (not sure it's the right translation, my xp is in french) and use the network configuration assistant. You will have to answer to some questions and I think you'll need your XP cds.

Perhaps you have a firewall program blocking the connection? When I initially hooked mine up that way, I had to configure Norton to allow the 192.168.0.0 subnet (I think that's the subnet that Microsoft uses for internet sharing).