Very strange Ping response times

I have a Win 2003 Standard Server acting as a Domain Controller. On this
machine I ping another computer on the network - sometimes the ping works
fine, other times it doesnt even seem to run but rather it just spits out
data immediately w/o even giving time for it to work. The data looks like a
normal ping respnse except the times are all wierd. Example =5103378ms or
even =-5103378ms.

Event logs look good except the Application log records constant 1054
Userenv errors stating that "Windows cannot obtain the domain controller name
for your computer network"

What could be causing this?

BTW - other than what is stated above, the server and the network are
working fine.