[Paul Huryk]

I think you should build something on your own - not too hard and you know exactly what is in your machine. Dell and others use garbage motherboards and power supplies that limit expansion.

I would recommend that you get an SSD when building along with a good motherboard (not much more, but will let you expand if necessary). You can reuse items like your old HDD (as data storage), DVD drive, case (if you want), and maybe even your power supply. You will definitely want a stand-alone video card (although you can add one in later), 8gb (or 16gb) ram, and nothing wrong with Windows 7 at this point either - most software works with it. I would suggest you get a quad core I5 processor as they offer performance to price ratio that cannot be beat.

The sky is the limit, but for $800 or a little more, you can get a butt kicking machine that can be expanded in the future and will keep you happy for at least 5 years.