Advice. What brand desktop?
It all depends what your needs are. You dont need a 6 core processor if your just websurfing and typing. Dual core and 4 core are the norm now. The Ghz is your horsepower more Ghz the faster the processor is but more RAM helps too. I bought my wife a macbook she likes it. You dont have to worry too much about viruses and if you ever need tech support you can go down your closest apple store and they can usually help you out. My wife has gone in there for some issues and they helped her out. The macs usaully run a bit more $$ as well. Im a PC guy cause I am a bit of a gamer and you can upgrade/customize easier. I built my own unit so no specific brand. I'm running a AMD 965 3.4ghz and 8G of RAM. When I use my wifes laptop everything is opposite. Like closing windows or the the command button but when you use often you get used to it. Try to get down to a electronics shop/apple store and test drive some and see what you like. Cnet.com is one site that does reviews on electronics you can check that out as well. Like 3406pk said you could always replace the hard drive for a cheaper and quick fix just need the windows discs.
Roger