Here's a complete build, including monitor, mouse, keyboard, and speakers.
Case: A nice, basic Rosewill mATX case. It's small, but big enough to fit your motherboard and everything. $30
http://www.newegg.com/Product/Product.aspx?Item=N82E16811147112
CPU: AMD Athlon II X2 240 2.8GHz; The same one you picked out, inexpensive, and perfect for your application. $60
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103688
Motherboard: ECS A780GM-M3; A basic AM2/+/AM3 board, with integrated graphics capable of decoding HD video. $60
http://www.newegg.com/Product/Product.aspx?Item=N82E16813135233
RAM: Wintec 2x1GB DDR2-800; 2GB will be plenty enough for you. $25
http://www.newegg.com/Product/Product.aspx?Item=N82E16820161030
HDD: 160GB Western Digital SATA hard drive. $40
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136075
DVD: LG 20x SATA drive. $29
http://www.newegg.com/Product/Product.aspx?Item=N82E16827136167
PSU: Coolmax CX-400B 400w; I've had no problems out of these PSU's before, and it's plenty enough power for what you need. $30
http://www.newegg.com/Product/Product.aspx?Item=N82E16817159023
Mouse/Keyboard: Microsoft Wireless Standard Optical Desktop 700 v2; $20
http://www.newegg.com/Product/Product.aspx?Item=N82E16823109182
Speakers: Logitech LS21; Nice, basic speaker/subwoofer set. These are blue, however, they're also available in green, black, and pink. $30
http://www.newegg.com/Product/Product.aspx?Item=N82E16836121028
Monitor: Sceptre X20WG-NagaII; 20.1" widescreen 1680x1050 DVI monitor; nice, high resolution, good looking, too. $110
http://www.newegg.com/Product/Product.aspx?Item=N82E16824112013
With shipping (depending on where you are. I'm in a little town in Florida, so your mileage will vary), it should come to around $480.
This build would suit your needs for a long time.
Good luck!