Here's how you can set up..
Go to Components > VirtueMart > Configuration > Checkout tab > Scroll down to the Thank You Page URL section.
Enter the URL of your thank you page in the Thank You URL field.
Do you mean this as suggestion how simpel it could be and we should add it this way? I fear it isnt that easy, it even can break payment plugins.
Ovisele, you can override the orderdone.php and add there a simple js, which redirects to your page.