Building a computer can be quite simple. But what ever you decide to do, buy a decent Motherboard!!!!! It is the mainframe of the PC and a decent one can make all the difference, the manual that comes with it is the most important manual, once the motherboard is set up the rest is a piece of cake. Most M\Bs are jumperless now, and so are easy to set up.
If you are building a PC from scratch think about future upgrades by this I mean, try and go for an ATX option rather than AT as this is the way forward using P\S2 devices, better still USB.
If you decide to buy a PC from Dixons or an other retailer like that, make sure it can be upgraded and that everything isnt soldered together, I learnt the hard way about that. Dont be drawn in by the £700 wort of free software, its usually c**p like Dr Hilarys Medical Guide and Mystic Megs Fortune Telling Guide.
I have seen manny of my friends happy with home built PCs and with ones from big chain stores.
------------------
Remember, life is not a rehearsal, so live life to the full!