To get the Tcl/Tk inter-process communications working,
I had to get rid of xhost and configure xauthority on
my account (and the same on Ingrid/obs).
Here's what you do:

1) get rid of every xhost machine line in your dot files
   (mine were in .xinitrc). Make sure xhost is set to xhost -
   (ie. don't do an xhost + either)

2) create a .Xauthority file on your account on linux with
   mkxauth -c

3) add a .xserverrc file (you can copy mine probably) with
   the following line:
   exec X -auth $HOME/.Xauthority -bpp 24
   (the -bpp 24 is optional and depends on what you were doing
   before to startx - in this case I had aliased my startx to
   startx -- -bpp 24, so here I put the -bpp 24 in my .xserverrc
   file and got rid of the startx alias.)

4) if you are running X programs on other machines and need 
   to give them permission to use your mahine's display, you
   need to make a .Xauthority file on those machines as well
   and merge into them (xauth merge) the entry for your machine
   you created in step 2. To get this, on your machine, do:
   xauth extract fred yourmachine:0
   then go to the other machine, and do an 
   xauth merge fred (after transferring fred, of course - in binary)
   then add the other machine's entry to your machine
   by running xauth extract on the other and xauth merge on your
   machine.

5) Exit X and restart.

6) everything should work as before and xhost should report:
   access control enabled, only authorized clients can connect