MOBO: 29.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130093R - MSI P4M900M2-L LGA 775 VIA P4M900 Micro ATX Intel Motherboard - OEM
CPU: 65.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116038 - Intel Celeron 440 Conroe-L 2.0GHz 512KB L2 Cache LGA 775 Processor - Retail - cheapest processor that met the 2.0 ghz requirement and mobo spec,
GPU: 29.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125073 - GIGABYTE GV-NX72G512P1 GeForce 7200GS 128MB 32-bit GDDR2 PCI Express x16 SLI Supported Video Card - Retail - cheapest fully dedicated graphics for PCI x16 interface. MOBO has onboard, so this isnt fully necessary.
Case: 27.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16811164089 - Linkworld PRESCOTT 437-01-C2222 Black SECC/SGCC MicroATX Mid Tower Computer Case 430W Power Supply - Retail
Optical drive: 26.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16827106078 - LITE-ON Black 20X DVD+R 8X DVD+RW 8X DVD+R DL 20X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM IDE DVD Burner - OEM
HD- 42.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16822135106 - Western Digital Caviar SE WD800JD 80GB 7200 RPM 8MB Cache SATA 3.0Gb/s Hard Drive - OEM - there were a few cheaper ones, but this was a more trusted brand.
Memory: 66.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16820141211- pqi TURBO 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 667 (PC2 5400) Dual Channel Kit Desktop Memory - Retail - hey, why not have the max supported 2 gb ram when it is so cheap? also, the link never seems to point back to the right componet for the RAM, so just bear with it.
OS: any free version of Linux will suffice.
Total Price: about 290 dollars
Total Price after estimated shipping: 340
Total Price after estimated shipping and cost of cables (because everything was OEM), keyboard, mouse and speakers: 380