http://forums.microsoft.com/technet/showpost.aspx?postid=1714300&siteid=17&sb=0&d=1&at=7&ft=11&tf=0&pageid=21

i haven't read all 21 pages of this but i wanted to input the problem i'm having as well that seems related:

ok, so here's the deal with whats going on, which i don't understand.
On my vista machine i have two mapped drives that connect to my server (windows server 2003 standard R2).
Now, I tried two things and figured out what the deal was:

1. I setup a FTP server on the Server machine and shared one drive on the ftp server. I then ran a FTP client on my vista machine and transfered a file from the server to my vista machine and got 60MB/sec!

2. I then set up a share on my Vista machine, logged into my server and transfered a file from my Server to the shared Vista folder and got 60MB/sec.

3. Back on my vista machine, I tried transferring a file from the mapped network drive (which is the same drive as my above 2 tests) to my Vista machine hard drive and got only 20MB/sec. Also, instead of going thru the mapped drives, i went thru the network browser (which essentially is the same thing i guess) and still got only 20MB/sec.

I have auto tuning off, firewall service turned off, and no anti-virus software running...also sending a file from my vista machine to the server thru the mapped drive results in 60MB/sec transfer...its only when im transfering FROM the server to the vista machine from the mapped drive or network browser that i get 20MB/sec.

so basically, FTPing into the server and transferring a file to my vista machine resulted in a fast 60MB/sec transfer....as well as sharing a folder in vista and accessing that share thru the server and transferring a file to the vista machine thru that share on the server machine resulted in a fast 60MB/sec transfer...

the problem lies when using Vista's explorer (mapped drives or not) to transfer a file from the server to the vista machine...which only results in 20MB/sec.
So something is up with how vista is mapping the network drives and something with vista is causing it to transfer slow when going from the mapped drive to the vista machine.

i also came across this site that points to a Microsoft release: http://www.neowin.net/forum/index.php?showtopic=563139