First of all, XP1600 means 1.4GHZ.
Second of all, I seriously hope you at least read the motherboard manuals, as this is the most frequently asked question by people. Your FSB MUST BE at 133MHZ or otherwise it will run at 1.05GHZ.
Sorry for being rough, but sometimes I really ask myself who bothers to research on what they buy and get informed.
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The sound of determination is the echo of will...