Recently i tried the GWPA installation in eclipse junos on window 7 64-bit and it worked. I download Eclipse IDE for Java EE Developers, 250 MB from here.
Make sure you have set the Environment variables before installation of Eclipse as mentioned in this document.
Once you are done, Click on Help menu>Install New software>Click on "Add"
Give some name along with "Location" as the URL : SAP Development Tools for Eclipse - Juno Software Repository (check below screenshot)
Press "OK"
Select "SAP NetWeaver Gateway Productivity Accelerator" > Click "Next"
shout if you face any issues.
Rgrds,
Jitendra