How do I check to see wether a user has already rated a thread
 

I am trying to create a similar thread rating system as on vBorg.

I want to display the rating-form together with the current rating, when the user has NOT rated yet, and only the current rating when he HAS rated.

So my problem is - how do I check to see wether a user already has cast a vote on the current thread?

I suspect something like

<if $userhasrated>
{Show rate-form}
</if>
{Show the current rating}