I would buy a multimedia computer with dual processors, at least a 512K video card, dedicated sound card (not on motherboard) and a TV tuner (or an extra slot to put one. It should hold two 1 GB RAM chips but have four slots to be expandable to 4 GB RAM You get so much more for your money with a MM desktop than buying an “empty box” for $400.
I think the cheap “mass marketed” desktop computers are a HUGE waste of money. Tell Frys or a hole in the wall local computer shop what you want and they will build it for you.
For backup, I use a dual processor ASUS multimedia Pentium III (circa 2000) with SCSI and the works (weighs at least 25 lbs) which will blow any current cheap model out of the water.
My main desktop is a (very expensive) 2006 Sony Vaio HD (w/1st gen blueray) multimedia desktop but its video card is on the blink right now and needs to be replaced. It also weighs at least 25 lbs.