Router issue

My router has 4 ports, d-link EBR-2310. If I plug in our Mac computer to one of the ports, the other 2 Windows XP computers get really slow loading internet pages & we get error messages like, "cannot locate address", "connection timeout" , sometimes will freeze the screens. The Mac computer does not have any issues only the PC computers. Any advice?

Than you,

Ron Potapchuk

Or, why would browsing the internet become so slow after we added a third computer to the router?

Thanks.

Does anyone think I might need a switch?

Thanks

Ron