Can multiple instance in a cluster share disk resources?

Is there a way for multiple SQL 2005 instances in a cluster to share drives for user databases.

Once we install our instances in the cluster using seperate disk resources. Can we then have multiple instances share the same physical disk for user databases only. This is for a test environment.

Thanks

Unfortunately that is not supported for each SQL instance you have to use a separate cluster group and it also means a separate shared drive.