Network problem with Vista laptop & XP desktop

I recently added my son's computer to our network via a wireless network card. We have a Netgear WPN824 Rangemax router, now with 2 wired computers & 1 wireless. Previous to this we had 2 wired & our Vista laptop on the network via it's wireless built-in & had no problem getting online on the laptop. When I added my son's desktop computer to the mix I had to leave the network unsecured or I couldn't connect. All 3 computers now have access to the internet & can be seen on the network, but now I can't get the laptop online. It sees the network, but never can connect. What do I need to do to get this fixed so we can get online with the laptop again? All the workgroup names are the same, I checked that. What else do I need to check? I'm lost with this one since Vista is different than XP with networking.