CPU Socket Size Dimension 4600?

A Dell 4600 uses a socket 478 CPU. You can still find socket 478 motherboards around, just not many. If you plan to reuse everything, you'll need to find an agp motherboard that uses DDR memory, and that can support 800 fsb processors. You may also need one with integrated graphics if your original 4600 did not have an AGP card installed, and you do not wish to buy additional equipment. You will have to buy a new cpu cooler, as the factory dell unit cannot be used on a non-dell board.

My advice though, would be to buy the original replacement motherboard for your Dell. They are a bit pricey, but can be purchased on Ebay.

Or, now would be a good time to buy a new computer, possibly a laptop if that suits your needs.