This tweak is also valid for any windows version, and I have heard other operating systems to include Linux.

Symptom:  10 to 30 seconds delay or maybe even up to 1 minute when loading any web page. Once a web page is up, full internet speed is available, also downloads are not affected by speed loss.  If you have TCP/IP version 6 installed this is highly likely the problem.

How to check if IPv6 is installed (Windows XP):  Open up the control pannel.  If it is titled "pick a category", click "switch to classic view."  Open "Network Connections."  Here there should be a list of your internet connections, they could be network cards, dial-up connections, or others.  Find the one you connect to the internet with, for example "Local Area Connection #1"  Right-click on its icon and choose properties.  In the middle of the properties window you will see a smaller window that is titled "This connection uses the following items."  Some of the common items are: "Client for microsoft networks"  "Internet Protocal (TCP/IP)" 

How to fix (Windows XP):  In this windows if you see one of the items labeled "Microsoft TCP/IP version 6" select it and click the uninstall button.  DO NOT UNINSTALL "Internet Protocal (TCP/IP)" this will disable your internet connectivity completely.

Other Notes:  As far as I know this will be the next internet standard, but for now using the standard "Internet Protocal (TCP/IP)" will work.  You shouldn't find any problems uninstalling IPv6.  You may ask how did this get installed?  IPv6 is listed in windows updates and could be installed this way.  I am guessing that IPv6 slows down web connections because most web servers aren't using it yet.