Windows 7 64bit and wireless N adapters

Ever since I built my current machine about a year ago I've had constant wifi issues with various adapters. I'm running Windows 7 64bit.

First was a Dlink DWA-547. It worked on and off at first with up to date drivers before eventually it stopped altogether.

I replaced that with an Asus N13 PCIe adapter, which with the current drivers would see the network and report as being connected to the network and the Internet, wouldn't actually do anything (no web pages, no local network functionality).

I replaced that with a generic usb Realtek adapter (RTL818CU). New drivers, same story.

All three are different chipsets (Atheros, Ralink and Realtek) with similar or the same problem.

As best as I can tell from trawling through other support forums, the problem seems unique to the 64 bit version of Windows 7; I also tested the usb adapter on my MacBook Pro running Windows 7 64 bit and had no luck with that either. My next step is to try it on my brothers 32 bit machine.

As a 'temporary' solution I installed the old wireless G card from my old PC, which unlike the above supposedly certified for Windows 7 adapters works best (i.e. does anything at all) but isn't ideal.

For reference the router is a Dlink DIR 615, though everything else I've ever connected to it has never had any problems so I don't think that's it.

This is driving me nuts and I'm reluctant to buy another adapter on the chance it might work. Has anyone else had a problem like this and found a solution?