http://us.battle.net/support/en/article/diablo-iii-system-requirements
pretty basic, you could build a 500$ desktop to meet these easy
[TABLE="class: stripesTable, width: 0"]
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WINDOWS
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[TH="bgcolor: initial"]MAC[/TH]
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[TR]
[TD="bgcolor: #E8E7E7"]Windows® XP/Vista/7 (latest service packs) with DX 9.0c[/TD]
[TD="bgcolor: #E8E7E7"]Mac® OS X 10.6.8, 10.7.x or newer[/TD]
[/TR]
[TR]
[TD="bgcolor: #EBEBEB"]Intel Pentium® D 2.8 GHz or AMD Athlon™ 64 X2 4400+[/TD]
[TD="bgcolor: #EBEBEB"]Intel® Core 2 Duo[/TD]
[/TR]
[TR]
[TD="bgcolor: #E8E7E7"]NVIDIA® GeForce® 7800 GT or ATI Radeon™ X1950 Pro or better[/TD]
[TD="bgcolor: #E8E7E7"]NVIDIA® GeForce® 8600M GT or ATI Radeon™ HD 2600 or better[/TD]
[/TR]
[TR]
[TD="bgcolor: #EBEBEB"]1 GB RAM (XP), 1.5 GB (Vista/7)[/TD]
[TD="bgcolor: #EBEBEB"]2 GB RAM[/TD]
[/TR]
[TR]
[TD="bgcolor: #E8E7E7"]12 GB available HD space[/TD]
[TD="bgcolor: #E8E7E7"]12 GB available HD space[/TD]
[/TR]
[TR]
[TD="bgcolor: #EBEBEB"]DVD-ROM (required for retail disc versions only)[/TD]
[TD="bgcolor: #EBEBEB"]DVD-ROM (required for retail disc versions only)[/TD]
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[TR]
[TD="bgcolor: #E8E7E7"]Broadband** Internet connection[/TD]
[TD="bgcolor: #E8E7E7"]Broadband** Internet connection[/TD]
[/TR]
[TR]
[TD="bgcolor: #EBEBEB"]1024x768 minimum resolution[/TD]
[TD="bgcolor: #EBEBEB"]1024x768 minimum resolution[/TD]
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[/TABLE]