HI Sheng
Sorry bout ure dsl. It's nothin to do with xp or sp2 or anythin like that.
First, check that u havent got spyware or trojans runnin in the background - these affect speed when accessing the net.
Have you enough memory and did you overclock your bios settings lately? These can all mess your pc and dsl speeds up.
Check with your phone or cable line that you have no line noise. They can adjust your settings their end to boost your connection speed.
Equipment and lengths of cabling and wiring in your home can reduce quality and dsl speed as well as packet loss and distance from the exchange you are using (I live in Ireland by the way and we use adsl broadband now. I have a very good connection and download speed here. Tweaked it a bit too)
After all that try using cablenut to tweak your registry settings but make sure you back up your registry first.
Here's a useful info site i found: www.dslmechanic.com/