I am trying to replace my motherboard

From my searching I find that it is a Nvidia 520LE.

With much tact and diplomacy, I would like to 'talk' to you straight up.

That motherboard is junk.
The motherboard is just an ordinary, ATX form factor motherboard. The most common used form factor size, used in personal computers.
Uses the Nvidia nForce 4 chipset.

By the time you buy an exact replacement motherboard, you will have spent the same, or more, than you could spend for a much better motherboard. (That will fit! Only the I/O shield at the back of the computer, may not line up with the motherboard below. The motherboard does come with an I/O shield anyway)

I found from my recent search also this motherboard,
1.http://www.newegg.com/Product/Product.aspx?Item=N82E16813135075&nm_mc=OTC-pr1c3grabb3r&cm_mmc=OTC-pr1c3grabb3r-_-Motherboards+-+AMD-_-ECS+%28EliteGroup%29-_-13135075

$70 US.
Instead of the Socket 939 processor socket, or AM2 processor socket, you have now, you will have an AM2+ processor socket.
If your processor you have now, is an AM2 processor socket model, it will work on this motherboard.

Your ram memory won't work. You have DDR ram memory. This motherboard uses DDR2 at 800MHz. (Or also can use DDR2 at 1066MHz)
This = a PLUS!

You can buy 2GB's of DDR2 ram memory that operates at 800MegaHertz, for $30 at Tigerdirect. (Patriot Dual Channel-PC6400. It's two ->1GB sticks of dual channel capable ram)

Uses the AMD (Nvidia based) 780G Northbridge chip, and the AMD SB700 Southbridge chip.

Here are the specifications of this motherboard straight from ECS,
http://www.ecs.com.tw/ECSWebSite/Products/ProductsDetail.aspx?detailid=866&CategoryID=1&DetailName=Specification&MenuID=1&LanID=0

You cannot always buy the same motherboards because as technology changes, so do motherboards. I checked the specifications of your motherboard, and it appears that you have socket 939. Socket 939 is no longer manufacturered, but I may be able to find a new mobo that is socket 939. I just replaced my own Asus Socket 939 with a Foxconn brand.

Your processor will not work with the new AM2 sockets nor will your RAM be compatible. If you would like me to locate a compatible board, email me at buffalonymann@yahoo.com