Your ping in online games has nothing to do with the specs of your computer. What influences ping is connection speed i.e. dial-up, cable modem, dsl, where the server is located in relation to where you live, and the server hosts connection speed. Even the type of game can influence how much importance ping has on a game. Although being under 100 is usually a pretty playable ping. If you are pushing 150 you will really start to notice.
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It might be something to do with your MTU size. However its most likely just a poor ADSL connection. I know that my Freeserve (UK) pings are usually in the range of 15-30 for british servers and more like 60 for servers in the US.