+3  A: 

If I understood correctly your problem boils down to the problem of finding the number of Perfect Matchings in a bipartite graph.

Items form the left set. Bins form the right. If a bin needs k items, you make k copies of that bin.

Now you form an edge between an item and a bin if the item is a possible candidate for the bin.

Now you need to find number of perfect matchings in this graph.

Unfortunately, this is a hard problem. Caculating the number of perfect matchings in a graph is equivalent to finding the Permanent of an associated matrix, which is #P-Complete. See: Computation of the Permanent.

Your best bet might be randomized/approximation algorithms.

Moron
http://en.wikipedia.org/wiki/Matching_%28graph_theory%29#Counting_problems seems to say that the problem can be approximately solved in polynomial time. Also, would this be a planar graph? Why or why not?
Paul Reiners
Thanks for the references. They're very helpful.
Paul Reiners
@Paul: Most likely it won't be planar, as I expect K_3.3 to be a subgraph.
Moron
...See Kuratowski's theorem on planar graphs for an explanation.
Moron