Ok m8, just press it 133 times times and you`re up to 800!
Your board may have spotted something it didn`t like in the RAM and downclocked it ... I`ve seen this and never suffered any repercussions from simply stating the RAM "as is".
I had some good experience OCing my old P4. Depends what it`s design is though. Is it a Prescott? If it is, it`s a hot chip and stock cooling won`t cut it.
I had a 3Ghz Prescott stable at 3.6Ghz, but to be perfectly frank, that makes it great for surfing, word processing, playing old games etc but obselete these days. Your board is LGA775, thought about a very cheap core two duo? Even a bog standard variant will out perform a P4 easily. Without checking prices, can be sought for around 35 notes?