Wireless connectivity. we have a desktop PC with XP with a belkin router and my old laptop with XP

Question

we have a desktop PC with XP with a belkin router and my old laptop with XP connected to it. all works fine, and when i set up the network about 18months ago i made it pretty scure it is all hidden and encrypted with WEP etc.
i bought my mum a compaq cq70~116 laptop with vista for her birthday yesterday and i am trying to add it to the network. after much fiddling around i managed to unhide the network and connect the laptop. although it is not properly connected it just says is has limited connectivity on the IPv4 and IPv6. all settings are the same as on my laptop but it still wont connect. i have tried rebootin everything, re-adding it to the network and cant think of anything else to try. please help! it seems a useless present at the moment and i have spent 12 hours trying to sort it out and wishing id never bought it now ha ha