If those are approximately the specs you are looking for, what you should do is search around and see how much it will cost you to build and compare(obviously). The above deal seems pretty good for 800 USD because it comes with the monitor and Vista. I just always get concerned with custom builds you buy online cause their support is usually very crappy and chances are the components they use are very low end.
If you did choose to go with that, I would ask the company if they can give you model numbers to all the components...or at the very least the motherboard...so you can check to see what stuff they are putting in and what expandibility options you have for the future. 800 bucks is nice, but if it is some low end board that you can't do much more with, then you are stuck with those specs.
What I would suggest if you want to check prices to build your own, is take the specs out of your head when you search for your build. Just start by picking a good motherboard that will suit all of your needs, then pick the parts and build off of the motherboard and fit the specs into your budget. Then if the motherboard at least has all the future support you are looking for, you can sacrifice some specs off the bat to save money and just upgrade your unit down the road when costs drop. For example, you could save money by getting just a single core 64-bit
CPU, but have a board that supports single core and dual core CPUs. Then a year or two when dual core CPUs drop in price, upgrade to a dual core then. Or maybe you don't care to have a 320 gig hard drive. You could save and go with a smaller hard drive and maybe get a better video card.
Once you have a good motherboard picked...all you do is pick the components that fit your budget and fit in your motherboard.
Right now I would get a board that supports DDR2 800 memory (if you build your own cause you won't find retailers that sell units with DDR2 800). If you check Newegg.com, you'll see that DDR2 800 is a very popular memory standard and there is lots of competition in that speed. Which means you have many more memory options and can probably find DDR2 800 cheaper than DDR2 5300. And it is also faster

But I guess it all depends on availability in the UK...
Does the UK have any sort of online dealer like Newegg.com? I know at Newegg, you can get an OEM version of Windows Vista for a good bit cheaper than the retail version -
Newegg.com - Microsoft Windows Vista 32-Bit Home Premium for System Builders Single Pack DVD - OEM You should be able to find OEM versions of Vista on Ebay too.
Also, don't bother with Microsoft Works. You can get a near identical equivalent (for practical purposes) of Microsoft Office here -
OpenOffice.org: Home The only downside to that is if you would need to open up and share your documents with other people. Other programs like Works or Word won't be able to read Openoffice documents. But if you just need a program to create and print documents for yourself, then that will be all you need. And it's free...
As far as barebones, it may be beneficial to you. It will still be more expensive that way than if you build it yourself, but still cheaper than retail.
As far as hooking up all the power components, you can't do it wrong. All the ports on each device are keyed so that you can't plug things in backwards.
The only real tricky part to building a PC is attaching the
CPU to the heatsink and motherboard. The easiest way to do it would be to get a heatsink that has a thermal strip already applied so you don't have to mess with thermal paste. Then the only "hard" part is actually securing the heatsink down onto the motherboard...sometimes it can be a pain. The rest of the build is just like putting a puzzle together really.
