How to read w2000 Security events

[comprepsrv]

Can anyone tell me how to interpret the successful 
and failure audits for security events in event log?  
They log different things but there is no info on what 
they mean, or what to do about it.  for example, my 
server that is also our firewall/gateway has entries 
that 'this user does not have access to this machine' 
yet I am the only one that logs in there.  Others say 
things like account change attempt etc yet I am the 
Admin here and never changed the username.

strange