OT: VOIP clients for Windows and Linux?

[Gaijin]

     Hello,
	
     I was wondering if there was still any old-fashioned, direct,
computer to computer VOIP clients out there that  *don't* go through
some 3rd-party service like Skype, that will run on both Windows and
Linux, or at least Windows, so a friend can do some remote
troubleshooting of my WinXP box.  I was hoping to just email or phone
this friend our IP numbers, input it into a simple VOIP client, and be
able to speak to each other while he troubleshoots my system.  I only
have a cell phone, and the battery is only good for about an hour per
day, leaving me up the creek if I ever need to dial 911.  All the client
needs to do is create a voice connection between two computers, without
any frils, IP to IP.  We both can't afford 20-odd phone systems, just to
stay in touch, and everything out there now seems to require that
everything pass through some middle-man or service that now has to be
paid for.  I'm wondering whatever happened to software like
see-you-see-mee, or whatever that video-chat program was called, that
was being used on IRC, or the old I-Phone software...wherever they went.
  I'm looking for the cheapest, free voice communications software that
there is for Windows, and if possible, that will also work on Linux.
Any clues would be appreciated.  TIA,

         Michael