I can even get a pc that's as powerful as one of thos Alienwares and cheaper than PCFormat's one. I've got some contacts that deal with second-handed stuff (only used once stuff)... Pretty neat, as my pc costed me E650,-
Asus A7N8X - Deluxe
Amd Athlon 2800+ XP
1024mb ram (ddr pc2700)
Ati radeon 9800pro
Hercules Fortissimo III
SunFlower 450W Dual-Light Fan psu
other cheap stuff
Ye wont find them cheaper
My experience: buy the cpu and motherboard at a store and buy the rest from other people. (I normally ask if I can see it working and I always keep a multi-meter with me (for cheap&broken psu's)).
For cheap stuff I usually visit
http://www.tweakers.net/pricewatch
It's a dutch site that lists the cheapest stores in The Netherlands.