Again, there are many VNC clients, of which “VNCViewer” (http://www.realvnc.com) is available for most platforms and I have found it to work well with TightVNC.
When you first run VNCViewer, you will see the following:
Enter the IP address of your Raspberry Pi, append :1 (to indicate the port) and click on “Connect”. You will then get a warning message. Just click 'Continue'.
The following window will then popup for you to enter your password (“raspberr”).
Finally, the VNC window itself should appear. You will be able to use the mouse and do everything as if you were using the Pi's keyboard mouse and monitor, except through your other computer.
As with SSH, since this is working over your network, your Pi could be situated anywhere, as long as it is connected to your network.
There's also a built in VNC app for the Mac OS X that you may be able to use without installing any software
From the Finder, select Go -> Connect to Server… and type vnc://192.168.1.10 (or whatever the IP is) to connect.