Long lag with Windows network
From here

(specifically noted to help with Snow Leopard / SMB / Windows Server 2008)

Launch the Terminal (Applications/Utilities/Terminal).

You can use the vi or the pico editors included with Mac OS X to edit the smb.conf file by typing sudo vi /etc/smb.conf or sudo pico /etc/smb.conf. [Note, as always when changing system files, back up the original first]

You will be prompted for a password, utilize the password for your admin account.

I used vi. In order to change anything within the file you will need to put vi into insert mode by typing the letter i (at the bottom you will see the word insert). 

Some handy vi editor tips: vi has 2 modes: 'Command Mode' and 'Insert Mode.' To switch between modes you use the letter i in Command Mode to switch to Insert Mode and when in Insert Mode you use the Escape key to switch to Command Mode. File saves are done in Command Mode and edits to the file are done in Insert Mode. You can search the file you are editing in Command Mode by typing /searchstring where searchtring is what you are looking for in the file.

Scroll down to the line use spnego = yes and change the yes to a no.

Continue to scroll down to stream support = yes and change this to no, on the line immediately below that says ea support = yes change this to no.

In the next group that says darwin_streams:brlm = yes change this to no.

Save the file by first taking vi out of insert mode by pressing the Escape key. Then to save the file and quit vi type :wq and press Return.

Restart your Mac.