There are many sites and forums you can hunt round that can offer advice and articles on starting from scratch right through to the ins and outs of tinkering, overclocking and custom builds.
I am a long-time member of forums.hexus.net where advice is readily available although there are no specific guides.
I'd also recommend forums.bit-tech.net where their guide
http://forums.bit-tech.net/showthread.php?t=173675 is probably as good a starting point as any.
One of the great things about such forums is that they include everyone from beginners through to seasoned system builders. This means if you want to build a PC for the kids to surf with, a gaming power-house or a subtle media centre for the front room, there's advice and experience in abundance.
Just like on these forums I'd advise you have a good idea of budget and intended purpose so that when you post your questions the locals have a good point of reference from which to offer the best advice they can.
Other than that best of luck!
I hope you throughly enjoy it