Talk to your friend. Have the friend that built your computer look at your build and make suggestions to upgrade but don't expect to have no lag occasionally.
I built the computer I have now and it runs everything at the highest settings and I spent 925 total for the guts at online providers. In the moors I have to turn my settings to low to medium when in raid so almost everyone has lag in those situations. Get good fans and a cooler. Best Motherboard you can afford, don't scrimp on the power supply. Do not get Windows 8.
There is lots of information online. Check CNET. Check build it yourself videos.
[URL="http://s1.zetaboards.com/LeavesOfLaurelin/index/"]Leaves Of Laurelin - Landroval and Laurelin[/URL]
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Makalaurë, Cotumo, Laurefindë, Witred, and Tulus!