You are really better off building your own, from off the shelf parts. You can get far better performance for less money AND the parts are interchangeable.
You might become aware that several manufacturers are selling systems with proprietary parts (like Dell) that can only be replaced or upgraded with certain proprietary replacement and upgrade parts. You can't use off the shelf parts to upgrade or repair (Dell) systems sold by these manufacturers.
I'm going to stick with my recommendation of a quad core processor, not only do you get far better cache memory (the processor never overloads), but reserve capacity to run media and other applications all at the same time. As you add more and more in the future, the system does not become obsolete for several years. It's a better long term investment.
I would rather spend $1000 now to find a state of the art system, rather than buy a system that will shortly become obsolete, or will easily cache/RAM overload, causing frequent buffering pauses while watching streaming video.
If you can watch an entire movie without any buffering pauses or freezing / jittering of the HD video, then your processor / cache / RAM might be adequate.
The audio quality of the quad core boards is also superior. You will find true surround / sub woofer outputs already on the board, that make a home theater system much easier to construct, without adding audio cards.
3 GB ram is not unreasonable, especially if you like high speed computing. The more the merrier, and again this gives you more buffering, and less buffering pauses. You can use 6GB if you care to move into a more expensive operating system such as Win 7. I will stick with XP for my own reasons, and economy.
The better video card costing around $150+ takes the load off the system resources, giving you higher resolutions in video, giving you true HD, allowing a number of software upgrades over the next many years, again avoiding obsolescence, regardless of whether you are a gamer or a media enthusiast. A good media system IS also a gaming system.
Therefore, it's better from a long-term standpoint and a audio video quality standpoint, and a anti obsolescence standpoint to save up some cash, wait a bit, and buy a better system which will be enjoyed for many more years, compared to a "minimal package" type system.
Speaking of 6 mbps DSL, It's the bandwidth of the phone line wiring that prevents it. Can you watch an entire streaming HD movie without buffering pauses? Well then, DSL might be OK for you. But where I live, DSL promises 1 mbps or 2 mbps and delivers 100 kbps on a good day.
All I have seen from DSL is wildly overstated claims of speed.