HELP! Server keeps locking up

I have a Windows 2000 server that has been having troubles now at
least twice a week where it needs to be rebooted. I get errors 2020
and 2016 (The server was unable to allocate virtual memory. )

I suspect some app has a memory leak and the server is running out of
RAM and other resources but I don't know how to pinpoint what app (or
service) is causing this to happen.

Are there any tools or utilities I can run that will help me figure
this out?

Fran