Wow, that's a lot more comprehensive than I thought I'd get, I thought I'd get a recommendation from the Dell website

Thank you both very much.
I meant a budget limit of about £800 and I should point out before it's obvious I know nothing about computers.
The problem is willcocks you've given me three choices, which is like 2 too many, should I go for the middle one?

For instance could you swap them about, say have the blueray commandergc recommended instead of the cheaper DVDRW or the bigger ram from the first but with the second spec (does that one not need a graphics card?) The first is like the second but with twice as good (and expensive) mobo and processor right? As I'm not a gamer would they be wasted on me?
But you'd definitely say any of those would be better than anything from Dell?
For comparison this is my current model,
http://www.ciao.co.uk/Fujitsu_Siemens_SCALEO_P_Athlon_64_3500_2_2_GHz__6852833#productdetailwhich was alright (till it started freezing up on me all the time) but sooo slow, so speed is important, if I have it on for a long time it won't seize up if I play music and watch video at the same time for example. I think lack of ram was a problem. Storage and sound also important.
Obviously I can't build it myself, if I took those examples into a computer shop and asked them to build it for me (- screen) with a Window 7 thrown in it would work? And be similar to what they'd suggest if I'd asked them?
Do you how much they'd charge to build it and how long it would take (more than a week?)
Do I need any additional software (like Nero for example) or I can I get it all free from the net?
Will my current keyboard, mouse and monitor
http://www.pcpro.co.uk/reviews/monitors/969/mitsubishi-diamond-pro-720work with them?
A few other questions, is it worth buying a new monitor, like I say I'm not a gamer, I watch a bit video streaming, bbc i player, youtube, would a posh monitor be wasted on that?
What about these new touchscreens, any use?
Also on the hard drive, why do people want two internal HDs, is it for back up?
Is it a good idea to ask for the hard drive to be partitioned and put the OS and programs on one and your data on the other as this makes your PC run smoother, true?
Is it possible to have too big a hard drive or too much ram, or is that impossible, like being too rich or too thin?
Sorry for the basicness of my questions!
I might give it a go if as you say these self assembled ones are no more likely to break down or be more trouble than the shop bought ones that I've gone with before.