You can use 2 templates on 2 sites. One template per site to a maximum of 2 sites.
A site being an individual URI (or www if you prefer - eg
www.example.com
) [on a side note whenever using a URI for an example if you want to follow the W3C "rules" you should always use the URI of
www.example.com
example.net or example.org]
You can download to your local computer all available templates but can only use a maximum of 2 templaes on 2 joomla / mambo sites.