(this is for PhpED 5.5.x)

If you edit Smarty template (i.e. combination of XHTML and Smarty syntax), PhpED colors the both syntaxes correctly. The problem is that tree of tags structure in the Code Navigator window doesn´t appear. It´s because *.tpl file isn´t defined as HTML type in Tools->Settings->IDE->Associations.

So you should define *.tpl as HTML type. If you do so, a tags structure in Code Navigator appears but Smarty syntax is no more colored.

Is there a way how force PhpED to color both syntaxes and also generate tags structure in Code Navigator?

Poky's request is still valid for PhpED 5.6.

How to force PhpED to display the HTML tree of smarty templates?

I agree that this would be an excellent feature for those of us who work with smarty templates. However, I can see that it'd be quite hard to actually implement because of the fact that a smarty template need not contain valid markup. In fact there can be many conditionals / iterators and so forth in the smarty logic that emit incomplete markup sections to create an complete document.
But +1 to the request if it were possible to parse the smarty logic and create a navigation tree from it!