Let me calrify this for you with a simple step by step
0. Install Joomla and Virtuemart
1. Download and Install AUP component
www.alphaplug.com/index.php/downloads.html?func=fileinfo&id=54
This is the point system manager, I really recommend you understand how it works, especially about its 'rules' concept before you go any further
2a. Install the plg_vmpayment plugin you purchased from Nordmograph and add the relative rules to AUP rules thanks to the AUP rule installer inside AUP rules manager.
2b. Install the VM2buypoints plugin.
Create a Virtuemart category to store your Points packages and create some points package products for a set price.
In the plugin settings you'll have to fill in the points package VM category ID so it knows when a product is purchased from that category , it has to be changed into points for the customer and added to his points amount.
Also fill the points/currency ration so that when a product is purchased from that category for a certain amount, script knows how many points have to be added to the customer account.
Feel free to ask anything if you need more help, but make sure you understant how Virtuemart and AlphaUserpoints component basically work as they are the 2 cores of the application.
Hope this helps,
Let me know