Joining files in Snow Leopard

Step1: Launch Terminal.app

Step2: type cd ~/downloads (or whatever the name of the folder your files are)

Step3: type ls (this is to show all the files in that folder)

Step4: type cat filename.avi.001 filename.avi.002 filename.avi.003 filename.avi.004 > filename.avi

Then wait for it to join the files, when it is finished, the cursor in the terminal will start to blink again like the way when you start it.