[thelist] Editing an existing mpeg video

[ww]

I hope this is the right place to ask....

i have a client with an existing mpeg movie that they want to use for  
a different community and have asked if i could replace the logo that  
appears in the bottom right hand side of the video with one from one  
of their other communities.

My guess is the easiest thing to do would be to place the new logo  
over the existing one in the video....Is there a program i can use  
(mac osx) to accomplish this. I have not worked with video much and  
am unsure about how to approach this.

thanks in advance,
ww