Been away for a few days and just starting to catch up again.
Reading all the posts since mine last Sunday, there is a great deal of useful advice here.
If you are going for a completely new PC, rather than buying components piecemeal as you can afford them, it would be a lot better to save up until you can afford everything and then buy it. Apart from the warranty issues, technology is moving on all the time and something that is ideal and decent value today probably won't be in a few months time. Either you will be able to get an item cheaper, or something better will be the same price. There is never an ideal time to buy a PC, you just need to get the best at the time and accept that something better is not very far away. This is the biggest argument for not buying something which is cutting edge - you will pay a very large premium and the same spec will a LOT cheaper in a few months time. An example is a first generation i7 CPU a year ago against a second generation i5 today. The i5 is a lot cheaper and probably more powerful.
My approach to building has been to pay to have a basic PC built to my spec and then add extra bits myself as necessary. It is not that I couldn't build one, but things can and do go wrong and it can be a "h**l of a job finding out what is causing the problem and fixing it. I have always used CCL in Bradford (
http://www.cclonline.com) and found their service to be excellent. You can specify exactly the components you want and they will build and test the machine for £60, which could easily be money well-spent if there are problems, or if you are not confident about what you are doing. They also offer CPU/motherboard/heatsink bundles assembled and tested if you want to go part way, as geting a good thermal bond between CPU and heatsink is crucial.
OEM hard drives don't come with SATA or power cables but you usually get a supply with the motherboard and cables are not expensive. Having just checked some sample prices, hard disks seem to have gone up a lot in the last couple of months, ostensibly as a result of the floods in Thailand. I bought a 2Tb Hitachi drive in August for £55.
I always used to specify an Asus motherboard but for my last two machines I switched to Gigabyte after reading some reviews. Both makes have been fine and I would recommend either. A Gibabyte board with a Z68 chipset can be had for around £85 including VAT. Before buying, read some reviews and check out the manufacturers websites. From your shortlist, you can download the manuals as PDFs from the manufacturuers websites and read them in detail to ensure all the facilites are what you want.
Mervyn
I was up half the night last night trying to find a supplier for all the parts I wanted, just 4... much more taxing than building your first PC I have to admit, finally I ended up getting each part from a different supplier after spending ages comparing prices and delivery rates 
