Alright, I came up with a couple of options that I thought might work.

It assumes that you'll be reusing your monitor and peripherals from your old computer.

Option 1- more of a kit (somewhere around $550 after rebates):

The barebones
A case and PSU

Windows

Optical Drive

You could reuse your DVD or get a different case/psu combo if you wanted.  I'm a little leery of the PSU in the combo if you later decide to get a big video card as an upgrade, but it should be fine with the kit mentioned.

Option 2 - more mix and match (about $625 after rebates):

Windows

Optical Drive

CPU/MOBO combo

RAM/GPU combo

PSU/Hard Drive combo

Case

With this option, you could reuse your old DVD to shave off $20 ish and buy a cheaper case (or get one locally) if you needed to cut down more.

Option 2 is generally better stuff - same mobo and CPU, but the video card is a good bit better and you get double the RAM.  You will have less HDD space, but it will be faster a faster HDD, and you could add in your old HDD one as a second drive if you need more space.   If you're planning on gaming with more modern 3D games (shooters and such), I'd think the extra money was worth it, and I believe that the GPU comes with a free copy of DIRT3 if that's your thing.

But if you're mainly building for something like Star Ruler, which is more CPU bound, both should be effectively equal, and it might be better to save a bit now, and then save up for a really good video card if you needed/wanted one later.  Plus option 2 has a lot of rebates, so your initial price will probably be more like 700 and you'll have to wait months to get the rebates back, which can be a pain.

Anyways, hope it gives some ideas if nothing else.

I just dont get it. Why is power so important (other than the obvious need of power for your computer)?

Remember when I said back on page 2 (how in my opinion) I didn't think you were ready to build your own PC.  What you need to do first is either take a basic computer hardware course or get yourself some decent hardware books (failing that......a lot of googling and some serious web-based hardware guides) and not just asking question after question on forums.

It is extremely easy to mess up when building a system and (again in my opinion) forum posts are no replacement for a quick-n-dirty hardware course somewhere or even basic web guides from some of the respected hardware websites out there.  (check back over some of the links others have posted for you)

Google is your friend.........

Just to answer your question in simple terms.  Power is the single most important aspect to a system build.  By ensuring that each component receives all of the power it requires consistently one can avoid frustrating things like spontaneous system reboots and or  hardware-related freezes/bluescreens/crashes etc.

Many of the above issues I have been tasked by clients to investigate/solve were traced back to systems that had received upgraded hardware components over the years but upgrading the PSU was neglected (to the detriment of the entire system).

While power output is important, all brands aren't created equal. No PSU lives forever, and the cheap, light ones tend to go out with a bang rather than a whimper.

If you don't know what brand to go with, the rule of thumb is "heavier is better", because that weight usually means bigger transformers and heatsinks.

Pretty much what you get is what you pay for.  Computer components are not all the same.  As with anything, you'll pay a premium for 'quality'.... which is why you can spend $300+ for just a keyboard .... and probably yet get a mouse/keyboard combo FREE in your packet of Wheeties...