I am currently getting a new system going with Windows 64-bit too, have found a compatible (free) antivirus program - avast!, available athttp://avast.com/eng/download-avast-home.html
AVG pro is also compatible, but the free version is not.
I have also found that Nikon software (which will not install on 64 bit Windows), can be made to, by (prior to installation), selecting the "setup.exe" program, right clicking, and selecting "compatibility" tab, and choosing "Windows Xp" in the "Compatibilty Mode" box, and then proceeding with the installation. This gives full functionality to Picture Project on the 64 bit system as far as I can determine, including installation of NEF plugins into Photoshop.
BTW Photoshop 7 runs just fine on the 64 bit system