Exchange 5.5 trouble

We've been having a great deal of instability with an Exchange 5.5 server we have. It was purchased a year ago, and it is running Windows 2000 server. It has AD installed and is our primary DC.

Ever since it's been our mail server, it's been fairly unstable. Every few months we have to reboot it. Every few weeks OWA stops working, and we have to restart the IIS services. The last few weeks have been terrible. We have to reboot the server every week, and this week we've rebooted three times since sunday!

I've compiled the symptoms, and i'm hoping that someone can shed some light on them for me:

DCOM errors: In the event viewer since July 22, there are over 40,000 DCOM errors. Event ID 10010, Description:
The server {6EE7E990-8CBB-11CF-BF69-080009B4DB7F} did not register with DCOM within the required timeout.
These occurred every 30 seconds until 8/3 (Sunday). The Exchange services stopped responding shortly after.

LDAP: I never changed the LDAP port for Exchange, and i understand AD uses the same LDAP port. Would this cause this rampant instability?

Windows Network Server service: Often when i find the Exchange services have terminated, this service is stopped. I cannot start it, as it reports this error message:
Could not start the Windows Network Server service on Local Computer. The service did not return an error. This could be an internal Windows error or an internal service error. If the problem persists, contact your system administrator.

Currently, I am no longer receiving the DCOM errors. I just changed the Exchange LDAP port to 390. Exchange is up and working (for now), but the Windows Network Server service is still not starting.

Any ideas on where to begin troubleshooting?

WHat kind of hardware is this server on?

I just realized you have your mail server on the DC as well- THis is generally not a good thing to do. I would suggest demoting the server or moving mail to a dedicated server for mail only.

I assume you have 2000 up to SP4 and Exchange up to the latest service pack, also?

I would also be weary about possibly the system memory.

I, too, agree that the server should not be a DC. We have ours as just a member server.

http://support.microsoft.com/default...b;en-us;275127

http://support.microsoft.com/default...b;EN-US;224447

Server is a dual P3 1.4GHz with 1G of RAM. It was new a year ago.

I have heard that it is not a good idea to have the mail server also be the DC. Is there a reason for that? I mean, we only host about 20 users, so it would seem overkill to have a $2-3K machine just for logging in users, you know?

So I assume it's not because of the workload, it's something to do with services conflicting or something like that? Would Exchange 2000 work any better? I just don't know if we're going to be able to sell them on another server if it's not absolutely necessary.

thanks!