DHCP Server causes high utilization

Hi guys

I have a NW5.0 server which also acts as DHCP server. Every know and
then
the dhcp server would cause utilization as high as 100% on the server.
Only
way to stop it is to unload and reload dhcpsrvr.nlm (version 3.01).
All
service packs are applied (SP6). The server also contains a GW post
office
and runs Arcserve 6.6 and Norton AV corporate edition.

Any ideas on what is happening? Or how to fix it?

Thanks
Ben