As an IT professional a lot of people ask me what kind of computer to get. So, I have found a video from Eli the Computer Guy that explains well what to look for in computers.

Unfortunately Eli still believes the old lie that you can't get a virus or spyware on a Mac. Don't believe that. Mac's get sick too. Mind you, this is an old video from back in Jan 2010. A lot of people believed that back then.

For more about that see About.com's Mac Virus FAQ, or this PCworld article from October, or this Computerworld article from last month, or just Google it. The biggest class of Mac malware is trojan horses, just like on Windows these days, and second to that is malware that targets an application like flash or Java or Office that works on both Mac and Windows. A trojan usually comes with other software so anyone telling you that a Mac won't get malware because you have to give it permission to install a program shouldn't be listened to. If you think you are giving your password to give it permission to install iWork and you are really giving it permission to install iWork and a trojan horse, then that piece of protection doesn't work.

Other than that one point I think Eli's advice is spot on.

A little bit of an update to his recommendations, He was right, even then, that if you are buying new and are faced with a choice between 32 and 64 bit Windows go with the machine with the 64 bit, but don't go 64bit on a netbook/nettop if it's offered, even though they can do it these days, the biggest reason for 64bit Windows is to get more than 4GB of RAM and no netbook ever made can handle that much RAM. 64bit programs eat up a little bit more RAM than the 32bit ones, so you want to conserve what little RAM you have on a netbook/nettop.

That said, 4GB should be a nice target number to aim for for RAM with expansion room to go to more when it's needed.
With hard disks, bigger is better. You can never have too much storage space... and pick up an external USB hard disk of at least equal size if you have a spare $100. This will be your back up disk you can set the computer up to make an automatic back up to the back up disk. Do not store anything on that disk, just the back up. believe me you will be happy you did when you need to get something from your backup that would have otherwise been lost. If you use the computer for a small business get at least 2 of these back up disks and rotate them out once in a while, connecting one to the computer and storing the other off site in case there is ever a fire.