Developers these fountain effects use any picture and an opacity as the base, the particle effect image is called: particle.png
Depending on what your going to do I have different bases
Wall node picture using square image.
http://www.imvu.com/shop/product.php?products_id=15945724
Wall node picture using rectangular image.
http://www.imvu.com/shop/product.php?products_id=15946548
Floor node picture using rectangular image
http://www.imvu.com/shop/product.php?products_id=15947406