As I have seen in Oracle certification matrix Forms & Reports 11g 64bit is supported under Windows7 64bit. So I tried to install it and to work with it. Unfortunately there are serious bugs in it, please read for more information MOS Doc ID 1395965.1.
After starting Reports Builder, trying to open "Data Model" or "Web Source" will crash the Report Builder
Impossibility to create a Query based on a Pluggable Data Source (PDS) in reports builder
Reports Builder spins on CPU (grabbing full power of one CPU) when "Copy/Paste" functionality is used in Layout Model
For 1./2. is a workaround to disable all Pluggable Data Source (PDS) in cauprefs.ora, if you don’t use that feature.
But for 3. is no workaround besides to use Forms & Reports 11g 32bit!