Clarification of the motherboard power connectors from the PSU

[Appolonius]

I am hoping to replace the existing, standard  600 watt PSU in my Z420 with a 750 W Corsair PSU in order to drive a new graphics card that may sometimes draw up to 250 watts.  Reading the blogs from many people who have trodden this path before me there appears to be several issues with doing this:

1. The power cable from the Z420 PSU attaches to an 18-pin socket on the MOB, not a 24-pin socket that is the normal practice for an ATX desktop machine. 
2. There are also references to a second, 8-pin power connector socket on the Z420 MOB.
3. There are several references to an adapter cable that attaches to the 24-pin cable from a standard - dare I say 'normal' ? PSU at one end and plugs into the 18-pin socket on the Z420 MOB, and several sites on the Internet advertise such a cable, explicitly mentioning the Z420.
4. I can find no reference as to what plugs into the additional 8-pin socket on the Z420 MOB.

Can anyone shed some light on this?  In particular i) is there any wire in the existing 18-pin cable that provides some function other than just power - such as activating a fan or even turning on the MOB when the wire goes'high'?  ii) Is there in fact an additional 8-pin socket that needs some cable from the existing PSU to be plugged into it, and if so what?  iii) To anyone's knowledge has any one succeeded in doing this?

I can find the answer to the second of these questions by looking of course, but that would involve removing quite a few components.

[Grizzlys2k]

Hp Motherboards are custom propietary...so if its not an standard ATX that will use a 24 pin socket....you wont be able to use any other PSU's to their motherboards...except the ones that are build and recommended for your particular model...sorry to bear the bad news!