where can i find the .etek folder?

First it's .eteks not .etek [;)]
You don't have to create it. To install a SH3P or SH3L file under Linux, right click on the file and choose to open it with the SweetHome3D program found in its installation folder.

is it possible to accelerate sweet home rendering (or rendering plugin: advance rendering) ?

Prefer the built-in renderer to the advanced rendering plugin. From David's tests, it's much faster. Please read also the FAQ How can I speed up the rendering process in photo and video creation panes?

how can i use sweet home under win7 (64bit) as 64bit-programm?

See the FAQ How can I adjust the memory used by Sweet Home 3D?