My recommendations:

AM2 Athlon X2 5400+ (cheap, cheerful and its AMD!)
2GB 533mhz (1066mhz in dual channel mode) dual channel kit
320GB Diamondmax 10 16mb cache hardrive (the one ive got! only cost £72!)
Sony-NEC optiarc 7170A 18x DVD drive (One of the best DVD drives out)
ATI X1600pro PCI-E or Nvidia 7600GT PCI-E graphics card (both hovering around £100 in price)
Any ASROCK PCI-E DDR2 AM2 10/100 LAN 7.1 Audio 4 RAM slot Nvidia Geforce 6600 onboard graphics motherboard (its cheap and cheerful plus it has all the features you'll need)