Overview of building a machine

Hi, could someone please tell me what parts i would need to build a machine,
i have looked on ebuyer and novatech and they seem cheap.

I have never built a pc before, how would i know what motherboard of RAM to
get.

I need to build 2 pc's

1st One - lots of RAM, Big Hardrive, cheap graphics card - used for photo
edting , office applications, web design etc.

2nd Machine - say 256mb RAM, 30gb hd - used for internet, office etc.

TIA

ASF