Retroanon3

My girlfriend has been saving her money for quite some time and decided she would like to buy herself a desktop. She wants me to help her pick out a computer. She's saved up $1200 for this so I'm going to make sure this computer is really nice. I have never built a computer before and I have no interest in doing so. I don't know anyone who can build a computer, so my question is this. What would be the best route to take?

I am thinking going to Best Buy or purchasing a PC off Dell.com (she told me she would like a Dell, but it doesn't have to be one). She also wants a flatscreen moniter which I know cost a pretty penny. I am thinking she should buy a PC with a flatscreen monitor and really nice components. She should get at least a P4 3.2 gHz, 512 RAM, 128 MB video card, CD-RW/DVD-ROM, and at least 80 GB of hard drive space.

Should I purchase a computer with some of these part included already and buy say, a higher end video card to replace a 64 MB card that might come with it. I don't know how hard it is to replace hard-drives, or video cards, etc. I have also heard that with certain components, when you first attach it inside the computer and you start up the PC, things need to be calibrated a certain way. If anyone could clarify all this for me, I'd be deeply grateful. =D