Nothing wrong with eMachines (I had one) or Semprons.
Nice mini case, there.
Core 2 Duo is the winner of the CPU race for now. It's the fastest, period. AMD is still a great CPU, though, as well as my favorite.
Check around in the General PC's and the High Performance PC forums to see what aothers are buying/building, as well as a few tutorials (with pix). Then, if you have questions or need recommendations, don't be afraid to post a thread.
My Rig: SABLE
Antec 300 Illusion / Antec EarthWatts EA650 650W / EVGA GTX 760 2GB
AMD FX 8320 x8 Black Edition / Gelid Tranquillo / MSI 970A-G43
Sandisk Ultra Plus 128GB / Samsung 840 120GB / WD Black 750GB / WD Green 1TB / WD Red 3TB
G.SKILL Ripjaws 2x2GB DDR3 1600 - Crucial Ballistix Tracer 2x2GB DDR3 1600
Win7 Ult 64-bit - Func MS3 Mouse - CM Storm QuickFire Rapid Mech Keyboard
R.I.P. Danny L. Trotter
... 14 Nov 1945 - 4 Sept 2009