I made a US-Greek keyboard layout for Windows.
After it's installed, you can simply hold down the right-hand Alt key (or the Ctrl key and the left-hand Alt key) to type Greek characters using the corresponding Latin letter keys. Otherwise, everything should work as usual.
You can download it here:http://sagittal.org/us-techn.zip
Unpack the zip file and run the setup.exe that's inside it. Then Restart. Then choose "US-technical symbols keyboard" as your current keyboard layout from the right-hand end of the task bar.
Use at your own risk -- no warranty etc. Let me know if you find any problems.