small office network

We have six computers that connects on a wireless network. We have a netgear wireless roueter. There is one pc connected to the router, the other laptops connects wirelessly.

All the Vista pc’s/laptops can access eachother, the Vista’s can access some of the XP ones but the XP ones cannot access the Vista ones at all (if this makes sense).

what do we need to do so that all the laptops/pc’s running either Vista/XP can access eachother??