Buying a computer system/buying office/work computer
I just got a BSOD and am worried that my old XP computer is on its way out. I am looking to buy new computers (possibly from Dell unless you strongly recommend others) for my business (property mgmt/real estate) but I'm not sure about several of the options including processor, windows version (7 Pro vs. 8.1 vs 8.1 pro), memory, hard drive, and MS Ofc software vs libre/openoffice. We use Quickbooks quite a bit (several companies files within QB), property mgmt software (currently RIS), and some spreadsheets along with word docs, etc. All three computers would be networked (not familiar with networking options). Thank you for your time.
I feel that it's important to point out that Windows XP is officially End of Life (it has been since April of this year), and should not be considered secure or viable for Internet-connected usage as a result. You can read more about it from Microsoft here: http://windows.microsoft.com/en-US/windows/end-support-help
Regarding a new computer, the first question I would have is how much is your budget.
To your other questions:
1) I have no problems at all with Dell; along with HP and Apple they're generally what I suggest for pre-built systems. They have generally good customer service, good build quality, and will generally honor their warranties. If your specific software ties you to Windows, Apple may not be an option for your usage needs.
2) Windows 7 and Windows 8 are both very capable, but depending on the applications you need to run Windows 7 Pro may be the best choice, as it offers XP Mode (which is explicitly designed to handle legacy office/business software that won't work properly beyond XP). You can read more about that here: http://windows.microsoft.com/en-us/windows7/install-and-use-windows-xp-mode-in-w
3) Memory, disk, processor, etc likely won't be worth much worrying - unless you're dealing with absolutely massive books or data-sets, modern processors and system configurations will likely dramatically exceed your system requirements. I would, however, suggest implementing some sort of data-backup feature (7 Pro and 8.1 Pro will both include the ability to do this) as these machines are holding what sounds to be fairly important information.
4) Networking with only 2-3 machines isn't very complicated - I would probably just get a decent router (I would suggest Netgear), plug everything in via Ethernet, and call it a day. Most routers these days support WiFi as well, so you could have that to support various mobile devices within your office too (For example if you have a smartphone that can use WiFi, it will likely be faster than using your mobile carrier's network, and it won't count against your data quota (if applicable)). Depending on what you do for back-up and unified file access (I'm assuming all of the machines need to be able to work on the same sets of files) may mean buying some additional hardware, but it doesn't sound like you're dealing with large enough volume/complexity to warrant having a separate server in addition to the desktops.
As far as MS Office vs OpenOffice, generally I'm inclined to suggest OpenOffice because it's free and offers good compatibility. However the newest version of Word and Excel tend to do things differently enough that you may see formatting quirks or have trouble with some documents generated by those applications within OpenOffice. If you deal with a lot of other organizations that are likely to be using Word and Excel, I would probably just get Word and Excel to mitigate any potential headaches. If the initial purchase price is beyond your budget, Office365 is another consideration: http://products.office.com/en-us/business/office
With clarification to the above, it'll be much easier to suggest specific kinds of hardware for you. Also, don't hesitate to ask any more questions if you need clarification.