AgentP,
Sorry for confusing you - the second post was a tip for Blade on how to control his two machines from a single keyboard/mouse as it can be damn annoying when you accidently hold the wrong mouse when looking at the other screen.
Back to your original questions....
A budget of £500- £600 should get you a machine that is pretty much good for anything, so long as you dont want to do hardcore games/databases/programming/processing. Building one yourself will be cheapest but is not for the faint of hearted.
My advice would be: -
1) Dont buy off mainstream highstreet stores - this adds alot of cost.
2) Dont pay for extra insurance for component breakdown as two years down the line most machines will have depreciated enough that it would be cheaper/more cost effective to buy a new one.
3) Pick your budget and look online at what you can get for that. Some good sites to compare are: -
1)
Computer Supplies and PC Components from Novatech
2)
Scan 3xs Systems - Custom Built PCs
3)
PC Nextday
4)
Dell UK: Laptops, Desktop Computers, Monitors, Printers & PC Accessories
5)
Desktop PCs - Computers - Windows XP Professional, Home & Media Center - Misco.co.uk
6)
dabs.com - Desktops & Servers products at great prices from dabs.com
4) Dont just look at price - look at the components you get for the price and try read reviews not only of the systems but the individual components. E.G. An ATI HD3850 graphics card is considered an old and mediocre card whereas the ATI 4850 is meant to be excellent. It may be worth spending that little bit more to get something that will last you longer.
Once you have narrowed down to a few machines you like the look of (and price of) feel free to start a thread with links to them on here and you will get some advice on pro's and con's with each system. Some people prefer brand names such as Dell and HP however with unbranded machines you can get more value for money (not always the case).
With regard to your question on external storage - how it is going to be used is important. If you just need more disk space then what system do you have ? it is very easy and cheap to add a new hard drive to an existing desktop system.
If it is an external disk you are after then you will need to consider speed - both USB2 and Firewire are very slow in comparison to your existing internal hard drive - USB3 (Due out last quarter this year/early next) is a fast alternative as is ESATA (External SATA) - both of these have implications in cost and availability - ESATA has been around a while but drives supporting this are not that common as are motherboards - Some E-SATA packages include an ESATA card to be installed in the machine. The benefit of E-SATA is that it is the same speed as your internal disk so there is no waiting on data.
If speed is not an issue then any USB2 drive will do that is within your budget - best to read the reviews of the ones you see - again look online for the best prices.
Cheers
Jof