If you have an intelligent switch check the switch for dropped
packets, collisions, etc. If you are seeing this or you don't have an
intelligent switch, try disabling auto negotiation on your switch port
(if you can) and the NIC card and manually setting the link speed and
duplex settings. Obviously you have the same settings (1000, full
duplex) set on both ends. Usually auto negotiation works correctly,
but when it doesn't you'll have no end to network performance issues.

A larger part of the issue is the Windows network stack. Microsoft
created a new stack for Vista and Server 2008, and smb/cifs file
sharing speed between Windows Server 2008 and Windows Vista is much
improved compared to older versions of Windows. I don't recall the
technical details, but this is one issue you'll run into with Windows
file sharing there there is no fix for other that going to
Vista/Server 2008. I haven't checked Windows Vista and a Linux samba
server yet. I should do that as I have a Windows Vista box and Windows
XP box on my desk and a Linux samba server across the room...

-- 
Andrew S. Zbikowski | http://andy.zibnet.us
IT Outhouse Blog Thing | http://www.itouthouse.com