Как мне установить Burg в Ubuntu 12.04?

При попытке установить Burg появляется следующая ошибка:

Package burg is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Package burg-themes is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'burg' has no installation candidate
E: Package 'burg-themes' has no installation candidate

Я использую Ubuntu 12.04 в качестве двойной загрузки с Windows 7.