The PicoScope 6 software is compatible with Windows 7 64-bit. Have you tried PicoScope 6.6.18 (Release Candidate)?
With regards to the second question, the dll that is currently supplied as part of the SDK for each device is a 32-bit dll. You would have to write a 32-bit application to use it. There are plans for 64-bit drivers but I can't advise on timescales at this present moment in time.