AQT v8 and v9 run fine under Windows Vista and Windows 7, both 32-bit and 64-bit.
To resolve this problem, right-click the installation file and select "Run as Administrator". You need to do this even if you are signed on with administrator rights.
Both Windows Vista and Windows 7 prevent users from creating files in the "c:\Program Files" directory structure. In some earlier releases of AQT, workfiles and queries were created in the AQT install directory; this will no longer work with WIndows Vista or Windows 7. In this case you will need to use other directories for these files. These directories are specified in Options > File Locations.