Some already mentioned this app that comes with XP but here's the command to open it from the run menu.
Services.msc, this lets you tweak all of the little Windows XP services, many times you don't need half of these. If you do turn off some of the ones that seem to relate to networking don't be surprised if you find it difficult to get a network up
Another tip, a straight format of your HDD will definitely freshen things up. Make sure to get all of your updates as soon as your online though, even if you have to take your tower over to a buddy's house.