What's the easiest way to move some files in a directory tree?

[Darin Strait <darin_strait@yahoo.com>]

Hello.

I have a large directory tree, with scores of end nodes. Each end node in the 
tree has a number of files whose names end either in .mp3 or in .flac. 

I would like to copy the directory structure of the tree, but I want to move 
files that end in .mp3 to the new tree and leave the .flac files behind.

What is the easiest way to do that? I was looking at unision, but unison seems 
to be copy-only; there doesn't seem to be move the flac files.

Thanks in advance,
-darin