Ok, this is very easy ofcourse for most of us, but anyway, just to help the beginners:
http://www.webmin.com/deb.html
1) SSH with PUTTY (http://www.putty.org/) - make sure you enable SSH in your OMV panel !
2)
3) dpkg -i web (then press TAB to complete the name)
4) apt-get -f install
Done !
You can now login to https://your_server_ip:10000/ as root with your root password, or as any user who can use sudo to run commands as root.
Regards,
Arthur