Im gonna upgrade my processor from the AMD Phenom 8450 (triple core) to the AMD Phenom X4 810 (quad core)... Do I have to format my drive even though its the same manufacturer and both of them are phenom (I completely understand if I HAVE to for driver reasons, but is it necessary?)
I would think you would not, because windows will just detect it after startup, but I am not completely sure of this, as when I upgraded from a A64X2 4200+ to a Phenom X4 9600 BE I did not
It's not necessary but i would recommend it just cause.
yep
ALWAYS reformat when you make a hardware change
its not always necessary for it to >work<
but you must format so that it works optimally
Not necesarry at all, since cpu does not use drivers what so ever and are auto detected.
I dont think it is needed either. 
Uh.... If that's true, then I've really screwed up lol.
I have to disagree. Tho, if somethings not working why not format.. but if everything works (which it should.) then there is no need to format
HAHA You need to format when you upgrade hardware.. That's funny, and a lot of crud. That's not true. I've added hard drives, graphics cards, ram, processors, dvd burners, and sound cards and I don't need to do jack, besides install/uninstall drivers, if [size= 13px; border-collapse: collapse; white-space: pre; -webkit-border-horizontal-spacing: 2px; -webkit-border-vertical-spacing: 2px][color=#ffffff]necessary[/color][/size].
I just went from my old system which was Â
Asus M2N-E SLi
AMD5600
2gb OCZ ram
EVGA 8800GTS
700w OCZ PSU
 to my new system which is
GIGABYTE GA-MA790X-UD4P
AMD 720
4gb corsair ram
ATi 4770
700w corsair PSU
and all I did was put my old HDD in and turned it on and had no problems. I had more problems when I tried to start with a new HDD and installing windows which is what I tried at 1st before saying fuck it and put my old one in.
Just make sure to remove old motherboard drivers and install new ones
You know that a triple core CPU is a quad core, but the other core is disabled, right?
I think he might know that man!