Take a look at this similar question:
Oracle 10 g developer
Assuming you are running Win7 x64. In Oracle Forms Designer it will by default load the x64 IE, you need to pick the x32 version. Edit, Preferences, Runtime, Change Web Browser location to the one in C:\program files (x86)\Internet Explorer\iexplore.exe
You may also need to change formsweb.cfg to drop jinit and use java.