4
In short: no. As you see, some of these vatiables, are specific to this main menu block. Thus, they cannot be called in another block.
<{$xoopsurl}> is a site wide smarty variable, but a custom block made through the block admin page is not a smarty template. You cannot use those Smarty variables in that custom block. You can add php code however, and HTML.
Horacio meant that when you're creating a real custom block, and add it to the module you want to use it in, you'll have to create a new PHP file with the block generation and moderation code, the xoops_version.php file (defining the block), and the template file. In that template file you can use Smarty variables.
So, basically, there are two options: a basic one with the blocks admin page, where you can use the XOOPS_URL variable as Horacio described, or your own php code, or you have the more advanced option, where you actually code a full complete new block and add it to a module (thus extending the existing module).
Herko