Great thing about AH is that you don't need the top of the line computer to play it. And there is plenty of help in the forum. We may not always agree on the advice but its free and plentiful!
Here's some general guidelines. Good CPU 2.6mhz or faster, Solid MB from good manufacturer(Asus, Gigabyte etc). Stay away from ECS. Hard Drive 7.2 or faster(WD, Seagate), Separate sound card(frees up some frame rate), Good Computer case like a Antec 900. Buy the best video card and monitor you can find. I think a 22 inch monitor is standard anymore. Video cards; Best card changes almost every two or three months so research before buying.