Hello, I have never used this software, but according to its description it has a real-time antivirus. You shouldn't use Norton and this one at the same time because both have real-time protection, it's very possible that this is causing the slowdowns.
Also their web page says that ad-aware pro is compatible with 64-bit vista:
Supported Operating SystemsWindows 7 (32/64-bit), Windows Vista (32/64-bit), Windows XP (32-bit), Windows 2000 Pro