It depends if you like AMD or Intel, AMD is cheaper, and offer more than enough performance for SCII, I used to play SCII on my 880G HD 4250 Integrated graphics on medium, But I just installed a HD 5770 and I can run it on ULTRA zero lag. You should start looking on a triple core and above. In general you can built an AMD system for less than 400. AMD Athlon ii X3 ~$75, MObo $70, Power supply $50, HD 5750 or 5770 ~$115-130, Case ~$30-50, 2GB Ram (for now) ~$20, HDD $40... thats $400. Then You can add Another 2gb ram, and a decent cpu cooler to overclock... or spend a little more on CPU and graphics its your choice. But That I think will run SCII on ULTRA, I am not sure if in a crazy resolution like 1920x1200. But in Full HD you should be fine. Specially if you spend a lil more on graphics side.