You have an Athlon II X2 and DDR2 memory, its an AM2+ socket, but the board has a BIOS that supports some AM3 chips. Looking at the Emachines site, it appears that most variations of that system came with an Athlon II X2 CPU, it likely cannot support more than a 65W CPU and probably doesnt have BIOS support for anything higher than an Athlon II X2, thats one of the down sides to prebuilts, they arent designed to make upgrading easy.
You know it can get quite complex but I tricked the operating system (XP) of an old 2006 era emachines T6420 (socket 939) into using a much newer type AM2+ motherboard with an Athlon II X2 240 CPU.
So I essentially saved my OS and applications and data off that hard drive.
How I did it was to replace the motherboard with a newer type one with the same chipset,IGP and same exact network chip.
You probably won't have to do this here though.
Here are some helpful links btw.
I think that your motherboard is an Elitegroup ECS model mcp61pm-gm rev 2.2
Here is the Elite Group website showing some NVidia 6150SE (I think your IGP/chipset) models (obviously yours is likely Micro ATX).These motherboards may not be exactly the same as yours but would likely have the same Chipset/IGP/Network Chip as your motherboard (so you could replace your board if you want to to have more or better CPU support).
It could quite possible that the maximum TDP on your board might be around 89 watts or even 95 watts.emachines could be using that CPU because they purchased so many of them in mass for production at a low price.
I've seen several Gateway models with motherboards with a maximum TDP of 89 watts yet are using slightly higher (not by much) 95 watt quad core CPU's in them.
If (IF) your board supports 95 watt TDP (probably tops) CPU's I would recommend using an Athlon II X3 450 CPU if your board will work with this ( a good possibility that it can).On these cheap motherboards I think it advisable NOT to consider over clocking the CPU's on them because the likelihood of them burning out would seem rather high.
The worst thing about emachines is that they tend to use cheaper (low power) power supplies.
I would recommend considering replacement in the future with a beefier more reliable brand.In the past some of them were notorious for not only failure but taking out the motherboard with them as well (especially the models around the 2006 era using I think the Bestec model power supplies)
If you replace your CPU with one that consumes a lot more power replacement of the power supply is really mandatory (especially considering that it's an emachines brand computer.
Just giving you some helpful hints here.
edit some other advise.
It would probably be best for you to keep the budget emachines as it is (use the same CPU) except replace the power supply with a more reliable more powerful one and perhaps get a discrete ($50 or so) Radeon HD 4650 graphics card for it rather than having to use the poor Integrated Graphics onboard.