You'd be looking for the Pentium 955 or 965, the 965 is the last and fastest one produced.

if i buy a c2d cpu, my bios turn on the option overclocking?

NO the XPS 600 will not run a Core 2 Duo. Look in the forum, several of us tried and it did not work.
You can overclock the 955 to 4GHz and the 965 to 4.26Hz though, basically 533MHz higher than the rating since the multipliers are open on those CPU's.

ok thank you, aemmmm - the cooling is enouth?

I personally upgraded my XPS 600 from the 840EE to the 965EE without any problems.  You need to have Bios A06 or later to support 1066FSB (used by the 955 and 965EE chips).  I also understand there is a different Dell heatsink for the EE chips.  I doubt it is necessary since the 965EE is relatively cool (for a Pentium), but I already had the EE heatsink so I can't really say.

One word of caution:  I know of at least one very knowledgable XPS 600 owner who tried to upgrade his machine to a 965EE and could never get it to work.  His screen name is CBC888, you might want to touch base with him by PM before you invest in a new processor.

i want to buy a intel D 960 with 3,6ghz

I would guess an upgrade from the 930 to the 960 should work.  Note, the 960 will not be overclockable on the XPS 600 in case that is important to you.

Where can you get the Dell heatsink for the EE chips?

Dell parts sells the EE heatsink, I think it's around $25.  Sorry I don't have the part number, you might PM CBC888 (I know he ordered one as part of his unsuccessful upgrade attempt.)

Message Edited by Teckinno on 01-17-200709:30 PM