I have Windows 7 RC installed, with a Hauppauge 1800 and an ATI AIW HD. For months I've been thinking the computer wasn't registering the Hauppauge card, since after tuner setup it would say one tuner wouldn't be configured, and after clicking 'details' it would reference a "Hauppauge WinTV 885 Tuner" or some such. Well, I removed the AIW and used the onboard intel graphics card to see if the Hauppauge would be recognized without the AIW in. Windows Media Center came up fine, no changes, and was still tuning in TV. So, it was the AIW all along that it wasn't registering.
I read a few other posts talking about the method described here for getting the right driver installed for the NTATIVLM61 device, but when I attempted to update the driver, letting Windows search for the driver, it would never work.
Instead of choosing the option to let windows search for the driver, I selected "browse" and pointed it at the directory where the latest AIW drivers had been extracted to (typically c:\\ATI). It found the driver there by searching subdirectories and installed it.
I reran the TV Setup in Windows Media Center, and it detected two tuners. Finally! Mystery solved.