How are you running scratchbox? Is it inside a virtual machine, or in a regular desktop linux install (Ubuntu?)?
By default, most linux distros don't allow remote X connections. You'll have to enable it in your display manager. For Ubuntu using GDM, edit /etc/gdm/gdm.conf. Change DisallowTCP=true to DisallowTCP=false. Then you'll need to restart you X session (Ctrl + Alt + Backspace or full restart). Then, you'll need to allow remote connections. You can allow all remote connections by entering "xhost +" in the command line, or "xhost + ipaddress" for a specific host.
If you're still having problems connecting to your xsession, make sure the port is open. Install nmap "sudo apt-get install nmap", and then test your computer "nmap -v -A localhost". If everything is setup correctly, you should see: "Discovered open port 6000/tcp on 127.0.0.1".