show block only if logged in

[SymbioteK]

I have a block of text i only want to show to logged in people.

How do I do this

eg

<show to members logged in only>block of text</finish only show to members logged in>

will be part of the header

[Lynne]

Usually something like:
<if condition="!$show['guest']">
stuff
</if>

or

<if condition="$show['member']">
stuff
</if>