Hello,
VM extension for JoomSEF is not a mambot! So trying to install it as mambot will not work.
It needs to be installed using the setup built-in JoomSEF control panel. (check there for icon install), The rest of the procedure is same as for other Joomla! installable components. (click it, select the file you have downloaded and upload)
Check JoomSEF documentation for details, the whole installation process is described there.
To Maljonic: We did not get any email from you. Where did you send it? VM extension has nothing to do with VM menu item. If you have JoomSEF 1.x you need VM extension 1.0.x. VM extension 1.1.x works only with JoomSEF 2.x. (it is written everywhere)