i wouldnt give 400 for it. maybe 300$
For the same you could probly build a I5
The system is about 350 after taking out a couple dollars here and there for them being pre-owned. OP see if you can lowball him or go with a PII rig. I5 wouldn't leave you with enough money for graphics and other essential parts. Unless you have other tasks to complete besides gaming you won't be crying over the measly 4-5 frames.
I put this together the last couple of days.
$70 AMD Phenom II 720BE
$53
http://www.asrock.com/mb/overview.asp?Model=M3A790GXH/128M
$70 Cooler Master GX-750 ( has 4 pci-e connectors so I won't have to get another PSU for a while) NEW
$40 Seagate 7200.12 500GB (These are the fastest 7200RPM drives out there right now) NEW
$45 Thermaltake V3 Case (I liked it but there are so many choices for cases under $50 on newegg) NEW
$15 Samsung 22X DVD/RW SATA Drive SH-S223C/BEBE (Black) (A steal brand new on Amazon for 14.99) NEW
So my total for everything: $293 and everything has free shipping.
I still have to buy a video card and memory and I plan on spending another 160 bucks between those two. So my total will end up being about $450 when that is all said and done. Everything is new besides the board and CPU. I have warranty on everything except the board.