Each computer manufacturer has different lines of computers. Each line is intended for different uses. Sometimes it really doesn't make a difference, but at times there are good reasons why the manufactures build machines for distinct purposes. In general, the machines designed for business use are slightly less high-performance, but are more reliable (they break less frequently).
My advice is to avoid these processors in red. They are inexpensive, sure, but you will hate yourself for cheaping out as you sit and wait for your PC to slowly chug through whatever task you are working on.
A word about cores :
A core is a processing engine. In the old days, each CPU chip had only one core, and the processor companies focused on making that chip run as fast as possible. Around 2004, they hit a wall, and needed to find a new way to increase performance without having to make their chips run faster and faster. So they started combining multiple cores into each chip. Almost all processors made today have multiple cores.
AMD's CPUs have an X2, X3, or X4 included in their names, which indicates the number of cores they contain. Intel has a little less variety.
Operating System :
Vista : All laptops built for home use and sold before October 22, 2009, will have Windows Vista on them. Vista is a huge, bloated operating system that requires significantly higher system resources to run at the same speed as XP. Also, Vista is less stable than XP, and there are still compatibility problems with drivers and programs - even though Vista has been around for over 3 years.
Windows 7 : Windows 7 is the latest operating system from Microsoft. It is basically a streamlined version of Vista, with all the rough edges sanded off. Unlike Vista, I can recommend 7. If you will be using your new desktop at home, or in any environment without a Windows Server, you will be fine with Windows 7 Home Premium Edition. If you will be using your desktop with a Windows Server, you definitely need Windows 7 Professional. If you get Windows 7 Ultimate, you can't go wrong either way.
PCs for business can still be ordered from distributors with XP as of December, 2009. All PCs come with either Vista or Windows 7, but some can be "downgraded" and will have XP installed on them. That is because Microsoft has required all vendors who sell their operating systems to include a copy of Vista or Windows 7 with every machine they sell.
Hard drive capacity
For general business use, 160 GB drives (which are about the smallest you will see) are more than enough - especially if you have a server where you will be storing most of your data. For a small increase in the overall price of the system, though, you can go all the way up to 1 TB (terabyte), which equals 1000 GB. You can even go up to 1.5 or 2 TB if you really need space.