Need Advice on Upgrade from P4 2.66 to 3.06

Might get a slight boost, but not worth the cost.
Your rig is pretty balannced now, and you would be better off saving up money for anther 6 to 12 months and then upgrading.

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The only reason for such an upgrade would be to get Hyperthreading.

If you do a great deal of multitasking then it might be worthwhile, but it's almost certainly pointless in this case (as with that gfx card your main focus would seem to be gaming).

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"Sex without love is an empty experience...
But as empty experiences go, it's one of the best" - Woody Allen

For not much more, you could get an A64 3000+ and a s939 mobo. That would make a difference. If you oc, you could easily outperform anything Intel has to offer.