You need to find a clean installer of Cubase LE/AI 6 demo first. It has been taken down from Steinberg, even from their ftp archive. Probably due to the large number of "free activations" being made from this version.

After install, open MySteinberg (Cubase e-licensing manager website) and register a username.
Opt for Cubase AI 6 (AI has more features compared to LE), and select Yamaha or Zoom.
Open Soft-eLicense (installed by Cubase) on your computer and copy your install serial thingy to your MySteinberg.
Let it generate your activation code. Use them on Soft e-License.
Make sure to update your Soft-License too.

There you go, free and 'legit' Cubase. No need to hack, no need keygen.