ports that listen-newbie questions

Please forgive my ignorance but I'm trying to learn about the
various ports that are described as being in a state of listening on my
windows xp system. From time to time, the OS requests to connect to my
ISP's domain name servers out of the blue (ie, not when trying to
resolve a ns lookup) & I was just wondering whether anybody here could
tell me what the OS is trying to do (I think that it's described as a
generic host process when it asks to connect)?
I've also noticed that my Epsom printer status program (that
provides me with neat little pictorial representations of the amount of
ink that I have remaining!)also regualarly listens on a port & again I'm
just curious as to why it should want to do that as I'm using a
stand-alone machine which I've configured to ensure that I'm not sharing
my printer or hard drive, yet the status utility listens on a port!
Aside from my curiosity as to what's happening, I'm also wondering
whether having these ports listening is good from a security standpoint?
Thanks in advance for any answers & for your pateince.

Tim Lister