I've got Philharmonic and SampleTank working in a 64 bit environment as well.
As Kenny noted, be sure the dll in in the scan path for Sonar.
I fought with SampleTank for a while. It would scan, and show up in the VST list, but I would get the "not properly installed message when I attempted to insert it. Turns out the problem was apparently related to UAC.
My solution:
Run the IK plug-ins as admin.
Find the SampleTank.exe file. I installed it to its default location, which was C: ProgramFiles(x86)/IK Multimedia/SampleTank 2.5.
Right click>Properties>Compatibility. Check the Run as Administrator box.
The dll is in Program Files(x86)/Cakewalk/Vstplugins.
I installed Philharmonic the same way, and both function normally.