If you sync at 4096 you get 4mbps speeds, that's how it works. The lower you sync, the lower your speed is.
Concerning the original post.
If you are running Xp, download and run this program on your pc, there's a guide as well:
http://www.iup.edu/house/resnet/winfix.shtm
If you are running Vista, do this, taken from:
http://grdead.ibloggie.com/reset-tcpip-and-winsock/
1. Check and repair Winsock corruption.
2. Click Start. In the Start Search dialog box, type: cmd, and right-click cmd.
3. Click Run as administrator.
4. Type: netsh winsock reset, and then press the ENTER key.
5. Type: Exit and press ENTER.
6. Restart the computer.
1. Reset the TCP/IP protocol.
2. Click Start. In the Start Search dialog box, type: cmd, and right-click cmd.
3. Click Run as administrator.
4. Type: netsh int ip reset, and then press ENTER.
5. Type: Exit and press ENTER.
6. Restart the computer.