I want to have a profile field where I can type in a text. Then there should be a second where I can type in a Post ID.

Then I need a postbit extension that the Profile field with the text gets displayed and if the profile field with the ID is also filled that there is a link at the text from the 1st field.

At the moment I have the following:
<div><if condition="$post['field5']">Test: <if condition="$post['field6']"><a href="[bburl]showpost.php?p=87&postcount=$post[field6]">$post[field5]</a></if></if>
</div>

[bburl] = url to my board

not quite sure i understand what you are saying do u have a screenshot or suthing?