Custom Service on Cluster

Hello all,
I have a bit of a problem with clustering. I have a 2 node cluster setup
on my network for high availability. There is a custom service (that one of
my developers wrote) that needs to run in the cluster, but can only run with
one instance at a time (it is a billing service) or it will double bill
customers. I installed it on the cluster, and it seems to have populated to
both nodes on the cluster. As a result, when it ran, it ran on both nodes at
the same time. This is not a generic windows service, so is there a way that
I can install this service on the cluster (virtual server) and have it run
only one instance, but fail over if needed? How would I do this?

Thanks.