So I'm looking at a core 2 duo upgrade....well actually a new system but I don't know what to do with my old system. I thought eBay maybe but anyone have any good ideas on where I could sell it and for how much?

water cooling system, involving the cpu, mobo, graphics, and hd
Asus p4c800-e deluxe
p4 3.2 northwood
512MB x 2 kingston hyperx DDR 500
Geforce 6800 GT
120GB IDE hd
DVDRW
DVDROM
Antec 420W psu
wireless pci card

planning on going to E 6700 1GB x 2, 7900 GT
Definately worth it, right?

Buying the Conroe E6700 is a waste of money, i would recommend that u would get the E6600 because it is cheaper and when u overclock it, it will pass the E6700 speed and didnt have to pay for the price of E6700

I'd keep it, personally - I can't even begin to count the number of times I've fixed an new machine using an old one (particularly hard drive/data recovery)

And yeah, the 6600 is a better buy than the 6700.

I haven't seen the pricing on them so I really didn't know, but thanks for the heads up!