Network vista to xp

Not sure how to explain this but will try.

I have two pc's with xp networked to my vista pc, they both appear in the
network window and also my vista pc appears, if neither are xp pc's are on
then nothing appears. I've just networked a XP netbook to my vista pc as
well and that won't appear unless one of the other XP pc's is on?

Now the funny thing is once it had appeared I made a shotcut for netbook and
even though nothing appears in the network window I can access it via the
shortcut.

Any help would be much appreciated.

Thanks

Eddy