You can just google flash cs3 remoting and there a many articles and some tell
you how to install it.
http://blog.vixiom.com/2007/04/17/actionscript-20-flash-remoting-with-flash-cs3/
There are better articles out there but this was the first one that came up.
Also some of your code will change because CS3 uses different veribage at some
places so again google and read.