Well, if the mATX case is going to be re-used I recommend a Biostar M7NCG-400. However, eMachines that came with the socket-A XP2000 were usually of the ECS VIA mATX chipset variant -- you can find it on the emachine website but like the dogs they are they charge about the same as a socket 939 Asus SLI board LMAO. If you want to be sure you can easily use your old OS-Restore CD's then you should first verify what mobo and chipset the system actually has. The Nforce2 emachines had FIC AU31 mATX NF2 OEM mobo in them and 333 FSB AXP2700-3000's- but I used Biostar M7NCG-400 twice in the shop as a drop in for those very units and it worked fine. The FIC AU31 that was sold with the emachine is nearly impossible to find, but if you have an ECS VIA board in there now it's very easy to find and replace (ebay).