From the level of computer savy your wife revealed in the other thread about fixing your current PC, I am guessing that you are not prepared to build your own system. That is OK. Don't be intimidated. Just buy a computer (from a reputable company) that is already assembled and ready to go. Spring for the extended warranty and virus protection... most of the new systems have free trials of a virus protection software, so you can try it before you buy it.
In my opinion, Dell is in bad shape right now. They were hit with a lot of lawsuits in the last year over selling computers with components that were known to be poor quality. The poster above who talked about his friend's Dell laptop failing 4-5 times in a year should be warning enough to run away from Dell. Apple (if you are OK with learning your way around a new OS) is a good choice. HP is a good choice (if you want to stick with a Windows system). Just my $0.02.
Edit: If you buy a Windows based system, you can usually save cash without sacrificing performance by getting an AMD processor rather than an Intel processor. If you research processor performance before you buy, you may see that the AMD based PC (whether it is HP, Dell, Acer, eMachines, whoever) that is $100 cheaper has the same performance as the more expensive Intel based system. Not always, but worth considering. Both Intel and AMD make excellent processors for Windows machines.
Also, your were wise to avoid buying Vista on your last PC. Windows 7 is out now, and is lightyears more stable than Vista.