What parts are neede to build a computer?1) Please post questions only once. I deleted the DUPLICATE thread.

2) Google response to your question: http://www.google.com/search?hl=&q=what+parts+are+needed+to+build+a+computer&sourceid=navclient-ff&rlz=1B3GGLL_en-GBUS430US394&ie=UTF-8&aq=0&oq=what+parts+are+needUsually...
Case
Power supply
Motherboard
CPU
RAM (memory)
HDD or SSD (storage)
Optical drive (DVD/CD/BD drive)
Video card if there isn't a video chip onboard or if higher performance is needed
Sound card if there's no onboard sound (very rare nowadays) or better sound output is needed
Network card if there's no onboard network (very rare nowadays) or a better card is needed
Cooling of some sort, at least a CPU heatsink & usually a fan, usually one or more case fans too

Hope this helps Added to Calums list: ( to make computer operational for a USER )

Operating System (OS can run off of Hard Drive/Solid State Drive, USB Drive, Optical Drive such as a Live Distro of Linux, Floppy Disk, or you can have it boot off of the PXE if Network Adapter SUPPORTS PXE ( most modern NICs do ) if you have a THIN Client Server running that is hosting operating systems for systems requesting PXE service. )
Mouse ( optional, but most builds have them, if a stand alone server not needed )
Keyboard (optional, but needed if not a stand alone server *If stand alone server and no keyboard is to be used after build, you will have to specifiy in BIOS to ignore missing keyboard at boot or your server WOULD not boot because it would hang at POST)
Display ( optional, but needed if not a stand alone server )
Power Cables
Cat5 Cable for Network if not wifi