Sam - not sure about Vista, but in XP, Network connections, right click on the internet adapter you have (dlink) go to 'properties' and on the 'General' tab select the adpater (at the top?) and 'Configure'. Take the 'Advanced' tab and what the gurus are saying (in Greek
) is to look at the speed/duplex setting or similar name. They are suggesting you don't use 'auto' but perhaps try 100 Full Duplex? It might be worth doing the same on the laptop to see what that is set at first? How did you install the new Dlink card? Did you select 'default settings?
You might wish to visit
D-Link 10/100/1000 Gigabit Desktop PCI Adapter, check you have the right drivers for that Vista version and see if there are any clues there.