Warning!!!!!
Do NOT do this unless you are NOT sharing files/printers
This does not/partially works on dial-up

1. Locate your Internet Conection (Start-->ControlPanel-->Networking-->Network connection)
2. Select it, right click it-->Properties
3. Uncheck or uninstall everything but Tcp/Ip (NetBIOS, NetBT, QoS, etc..)
4. Reboot (Note the differences from here?)
5. Browse Up and download faster

Why to do this?
Because NetBIOS and NetBT were never meant to be on-line, they're UN-SAFE and UN-NEEDED protocols, they were developed by Ibm in the 90's start, it was supposed to connect ONLY a private network with 5 to 15 computers, no more, and, for going on-line (being safe) it would have to be designed with more complex level of security.
If you want to read more, go to:
http://www.grc.com/su-techzone1.htm
http://www.grc.com/su-explain.htm
Those documents are a little bit old, but still apply (to Xp, i don't know if they apply for Vista).
I have being researching and there's a way to disable wins protocol (another un-safe protocol) from the network adapter but it's a little bit more complicated
This instructions are for Windows Xp, the site has instructions fir NT and 95/98