> I installed Python 3.2 first and then 2.7
This probably made 2.7 the default Python.

> I tried to open a .py file that's written with 3.2,
> but it were opened with the 2.7 IDLE.
So this is normal.

> So I uninstalled 2.7 and tried to open it again.
> Now the context menu were missed.
The uninstallation process probably removed the context menu.  If the 2.7 entry overrode the 3.2 one, once it's remove there are no entries left.

> I tried to open it over "Open with..." with other applications.
> I re-installed 3.2 and also repaired it, but the "edit with IDLE" is still not there.
If the installation process adds the "Open with IDLE" entry, it should do it again when you reinstall -- unless something got corrupted somehow during when 2.7 got installed on removed.