Are you using the latest driver for your network adapter? Go to the manufacturer's website to check for more recent drivers.

Is the slowdown occurring only while music or video is playing? Windows Vista Service Pack 1 (SP1) fixes a problem with network slowness that can occur during music or video playback.

Is TCP autotuning disabled or normal? Try disabling autotuning by following these steps:

1. Click the Start button .

2. In the Search box, type command prompt.

3. In the list of results, right-click Command Prompt, and then click Run as administrator.  If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

4. Type netsh interface tcp set global autotuninglevel=disabled, and then press ENTER.

5. Restart your computer.

(To re-enable autotuning, type the command netsh interface tcp set global autotuninglevel=normal, and then press ENTER.)

Are the capacities of the router and the network adapter compatible? For example, if the router is 10/100, but the network adapter is gigabit Ethernet, the network will transmit at the lower speed. You will need to replace the slower device to get the higher speed.

Are you using a wired connection? Try modifying the flow control setting by following these steps:

1. Open Device Manager.‌  If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

2. Right-click the network adapter, and then click Properties.

3. Click the Advanced tab, and then click Flow Control.

4. Under Value, select Rx and Tx Enabled (in some cases, this might be called Auto or Rx/Tx Pause), and then click OK.