In the download page (http://virtuemart.net/downloads) instead zip modules - are tar and gzip - this is a bug or so and conceived ???
No, that is the correct package to use for Joomla, as tar.gz packages are smaller in size than the equivalent zip. The package needs to be small as so many people use cheap hosts with a low upload_max_filesize of 2Mb and Joomla can usually unpack tar.gz for installation.
However some badly set up hosts cannot handle tar.gz at all and require zip. A workaround for these is to unpack the tar.gz locally and repackage as .zip, but the best option would be to get a proper host!
Alternative file packages are on http://dev.virtuemart.net/projects/virtuemart/files
Thank you .