This is stuff I've already done : Slow network browsing in Windows XP , Speed up Windows 2k/XP network , Hide the Scheduled Tasks and Printers folder in the network share view , InfoCellar XP Home Networking Problems
Part of the problem may be that the music folder has many thousands of files in it, and the MS network file system may have some kind of retarded N^2 thing. I am already hitting that fucking NTFS stupidity on the HTPC machine in which NTFS just fucks up completely on large directories (the directory B+ tree gets scattered around in fragments).
It's possible Windows network use is just retarded, like it sends 10X as much net traffic as the number of bytes you want to send.
BTW robocopy is pretty cool; I like the syntax of (from dir) (to dir) (file filter).