I want to use the default magento product list block and template but use it with my own custom product collection.
The collection is not part of a category, but a collection that is being created by my own module.
how do i tie the two up?
You need to create your own block class, inheriting from Mage_Catalog_Block_Product_List, and to override at least its _getProductCollection() method, to make it load your collection.
And regarding the template, you can assign the default one to your block in your layout definition.