The problem is most likely caused by Vista's new-fangled network stack. This automatic tuning of the Vista network stack sounds great in theory.
The problem is that some clients don’t support TCP window scaling or don’t have it enabled. Additionally, some firewall products also don’t support it.
In either scenario, the result is dropped packets, which can cause dropouts and slow preformance.
If using McAffee uninstall and turn off IPV6
Do this opening up an Administrative Command Window
Right-click-Run as Administrator and type in the following command:
netsh interface tcp set global autotuninglevel=disabled
You may also need to type in:
netsh interface tcp set global rss=disabled
Some Other Tips for Slow and Poor Access:
1. Disable the Windows Explorer Navigation Pane. To do that, Click Start, and then click Computer. In the top menu, select Organize, Layout, and then click Navigation Pane.
2. Map a network drive to the folder that contains the files that you want to copy. To do this, you may have two options.
1) Click Start, right-click Computer, and then click Map Network Drive. Type the path of the network folder in the Folder box, and then click Finish. For example, type \computer_nameshared_folder_name, and then click Finish.
2) Start a command prompt, and then map the drive by using net use command, for example, Net use H: \chicagotech/shared, where H: is the letter of the drive that you want to assign to the shared resource.
3. Use Robocopy or xcopy. For example, type the following command at a command prompt, and then press ENTER: Robocopy source_path destination_path file_name
4. Disable the automatic adjustment for the TCP window size on the network. To do this, follow these steps: Click Start , type cmd and press Enter. Type netsh interface tcp set global autotuninglevel=disabled at the command prompt, and then press ENTER.
5. Disabling Remote Differential Compression. To do this, open Control Panel>Add Remove Programs>Turn off Windows features, uncheck Remote Differential Compression.
6. Vista Index can be the issue too. If the Index have more collections, it will run more faster. You can modify the Index options. Or for the test, disable the Index feature from Add/Remove Applications.
7. If you have external drive, try to upgrade the latest firmware.
8. Also security and anti-virus can be the issue too. Make sure the software is Vista compatible. To test it, disable them temporarily.
9. Check the hardware such as NIC and switch settings. Make sure the speed duplex are matching.
10. Microsoft has an update is available that improves the performance and reliability of Windows Vista
http://support.microsoft.com:80/?kbid=938979 The changes take effect straight away, with no reboot needed.