Duplicate IP / Windows 2003 DNS

We've got a couple of funny issues here so I would appreciate a pointers in the right direction...

3 DNS servers on the network (2003 Domain) and quite a lot of dumlicate IP entries.
1. Scavanging is not enabled on the DNS - so I guess it can greatly contribute to duplicate DNS entries by keeping the stale entries. (Am I right about it?)
2. Some times when I ping some ip addresses with -a switch DNS server returns the names that even dasn't exist on the network. (No idea why it happens)

Is there any checklist of thigns I should check on the DNS to make sure it works properly? (besides n\making sure DNS points to itself)
Any recomendations as to what should I do to rectify the issue?

Thank you.
Elijah