So many possibilities, so little time... 
Few things I can think of to check / consider?
Multiple dispatchers on the same server?
Are they using (nolock) in queries?
Take a look at some of Chris Krabsetsve's blog posts. Tons of stuff there as I recall.
Also take a look at IdM Thoughtplace: Some thoughts on database locking in Oracle and Microsoft SQL Server I think there could be some stuff there too.
Matt
PS also check: IdM Thoughtplace: Calling all Dispatchers