The main difference between Dell's (and other makers') home and office lines is how they are intended to be managed. In an enterprise environment, PCs are centrally managed through a variety of methods, which include Winlogon, SMS, and Domain Group Policy. IT managers in these environments generally don't want end users messing with the configuration of their systems, so they buy machines with safeguards built in. The Dell Optiplex line, which is sold for business use, has some hardware features that PCs sold for home use lack. One of these is a chassis intrusion switch that alerts the systems administrators when someone has opened up the computer - e.g., to steal memory chips or tinker with the hardware. Another is a jumper or switch on the motherboard that is used to prevent unauthorized users from going into the BIOS setup. The case on my Optiplex 270 here also has a hasp for a padlock, in case the IT guys want to get really fussy about how much access they give end users.
Such machines are also outfitted somewhat differently. They typically have smaller hard drives than home machines, because most corporate environments rely on network storage for documents and databases. The local hard drive is used mainly for applications in these cases. I have a DVD-rom drive, but not a burner, another typical setup.
Corporate machines are also set up with professional versions of Windows, e.g., Windows Vista Business as opposed to Windows Vista Home Premium. They also tend to come without any bundled applications, a.k.a. crapware.
Should you consider buying a business PC? Absolutely! You will get everything you need to do your own system administration. You can order the machine with a bigger hard disk and any other peripherals you want. It should come only with the OS installed, leaving you free to load whatever you want in terms of security applications and productivity software. The downside to this is, you'll find it difficult to upgrade the components if you decide you want, say, better video for gaming, or premium sound for multimedia applications. But if all you're looking for is a general use machine, they can be a good choice.
A tip: if you want to buy a business computer, look for one that's off lease and has been factory refurbished. You can generally get very good deals on these.
