Windows Domain Controller Overloaded by Mac Logins??

We have three student labs running Snow Leopard in a Magic Triangle setup. This year we noticed that our Windows Domain Controller, which is quite a powerful machine, is suffering from cpu overload spikes at the beginning of each class period. It goes to 100% cpu utilization for 10-15 minutes at a time. Investigation revealed that the DC is getting hit by inefficient LDAP queries issued by the Macs. That is - queries that are not using an indexed data field and thus forcing the server to sequentially search the entire directory. There is an Apple documented issue with Leopard querying using MacAddress as a key. But that is not our problem. Our Snow Leopard Macs are instead querying using something called RID as a key. Has anyone else seen this problem and found a solution? Thanks!