How do check for listener services on a computer?

I'm running a little utility on my Windows Server 2003 called PortPeeker.  If I configure PortPeeker to listen a high-number port (like 5678), it runs w/o error.  If, however, I configure it to run at ports 21, 80, or 3389, it produces an Access Denied error.  (See image.)  I suspect this error occurs because there are services already listening at these ports.  

Does this make sense?  

If so, how do I inventory the listener services on a Windows OS?
Who is Participating?
Andrew OakeleyConnect With a Mentor ConsultantCommented:
from a command prompt
#>netstat -anb > netstat.txt

then open netstat.txt with notepad. It will show you all the listening ports and the app/exe listening on them
jdanaAuthor Commented:
Ashok DewanFreelancerCommented:
you can also use third party tool to view network connections

currports , its free

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