Nope. Generally speaking you must have two matched GPUs with the same chip. Here is a SLI faq list from nVidia:
FAQ On the up side you should be able to set up the weaker card as a PhysX card if you are interested in going that route. Here is a list of games that suppoert PhysX:
PhysX Games List And here is a PhysX faq:
PhysX FAQ