That condition should work wherever you want to put it in the postbit.
As for using options, you'd have to turn on debug mode and add the option to the dropdown you want to add it to. If you called it 'OTST_weekly", then you would change the condition to something like:
HTML Code:
<if condition="$post[userid] == $vboptions['OTST_weekly']">
an image
</if>
I haven't tried anything like that, so you should test it on a test site first.