Can you access pages normally if you hook PC & router with a cable? If so then the MTU for the wireless interface may need adjusting. click here
TCPOptimizer is mentioned in on that site but whether it's compatible with Vista x64 I don't know.
Sometimes Vista's TCP auto-tuning feature can cause problems, and it may be worth disabling IPv6 in the Network Connections panel...sorry, not using Vista at the moment so my terminology may be a bit off.