Dell is still a good company, but really, don't bother with their home division, skip strait to their small business division.
Dell Small buisiness is honestly a joy to order from, I would suggest calling them to order. From my experiance, with both ordering and service you get to speak to someone in the US, and you can usually bargain a bit with them, resulting in a lower price for you

. The computers come without the usual crapware, which is nice that you just get started without deleting a bunch of stuff you will never use. You can also get in-home service from a service tech, no need to send your PC out before you know what is wrong with it.
Although some Mac's have really nice build quality (the unibody mac books), it is just not worth it to me to pay that much more just for the name, OS, and build quality, two of which I have absolutely no need for

. With a mac, you also tend to get less hardware power for your money, which, as someone who builds computers for myself and friends/family, makes me rather sad

.
I would personally suggest staying with windows, if only for the reason that it is what you are currently using. It's easier to get used to it if you are already comfortable with what you are using. I have tried using OSX, but I have never really gotten it, mainly because I am so used to windows and linux, I have no need for it. Just a tip as well, if you don't want to use Windows 7 (which is really extremely good), Microsoft has extended the downgrade period for XP, so you can still get XP if that is what you want.
I will second openoffice if you don't want to deal with paying MS for Office.