OK, well first of all don't worry about asking what might seem to be silly questions - before you pay your money is the time to make mistakes and ask questions, not after!
So let's clarify what your objectives are, rather than your PC spec as such. Once you are clear with what you want to achieve, you'll be much happier with the result.
It sounds like you want a PC for gaming, which is great. Do you want to do anything else with it, like video editing? I'm sure you'll want to do some web browsing etc, but it's worth being clear at this stage.
Does the size of the base unit (the actual "computer") matter to you? Do you fancy a small 'shuttle' type, or is a large tower ok? Do you want it to be portable? Or even just 'lug-able'?
How about noise? Would something that sounds like an old fridge freezer bother you, or would you find the benefit in near-silence?
What about power-draw? I'm guessing that with that sort of budget it might not make a difference to you, but you might be an environmentalist at heart :)
The other questions i have for you relate you your previous experiences, which from the sounds of it are quite out of date (not trying to be nasty, just honest).
When i got my 20" widescreen monitor, my initial thoughts were "wow thats big" but i soon adjusted, and now cant wait to get something bigger. You are aware that the Scan spec you posted above had a 26" monitor? I'd love a 26", but in a small room (particularly if it's a 'family' room) it might look out of place. It all depends on how much you want or are happy to have the PC 'stand out'.
Your idea about a lower resolution for 'pro gaming' probably was true back in the dark ages (2004), however computer grunt has come on to the point where modern games have to be turned up to maximum (not just resolution but also the in game effects, and AA etc) just to start to tax it a little. And by 'a little' i mean, in the case of a 4870 or 280GTX dipping below 60 fps in most games at 1920 x 1200 resolution. You could almost argue that graphics chip makers are developing themselves out of a market since nearly all graphics cards from £50 upwards are easily good enough for 1280 x 1024, and the next generation £50 will comfortably do 1680 x 1050 i'm sure. So spending £250 on a graphics card means you absolutely have to game at 1920 x 1200 AS A MINIMUM, if not going the whole 30" hog!!
A current Radeon 4550 (
costing £40) would wipe the floor graphically with a 5700 ultra, as well as wattage-draw, noise polution, heat production, size... you get the idea.
As for widescreen 'efficiency' (ie how common or good it is), again back in 2004 it was a real hassle. Check out
widescreen gaming forum for all the 'hacks' that had to be developed by players to get things to work semi-ok (DICE were absolutely
rubbish with their stance on Battlefield 2). But again, that was then and this is now. Widescreen is not just the future, it's the present, and i'd be surprised if anyone was seriously considering a 4:3 ratio monitor for their next upgrade.
My other, more general rule of thumb, or to consider the peripherals
first. By these, i mean specifically the monitor, speakers, mouse and keyboard (plus webcam, scanner, printer and whatever else). Spend around a third (oe even half!) of your overall budget on these, because they should last you longer then the internal base unit components which will devalue quicker. A good monitor and speakers should last you years.
Hope that helps, i'm happy to give any more advice if i can.
