You should get the i915G chipset based motherboard, with a 2.8HT processor. Get at least 256 MB RAM, buy 2, 128 MB modules so that you can run them in dual channel mode. Get atleast a 80 GB SATA drive. Get a GeForce FX5200 GFX card if your budget permits, and if you want to play heavy games, otherwise the onboard graphics controller is quite good to play the latest games at low settings. Get a 17" Samsung Syncmaster again if your budget permits get a flat screen. Get a optical mouse from Logitech, its the best. And a multimedia keyboard.
Go for a Asus 2800+ with a MSI motherboard(This is a bundled package) with onboard graphics which should be enough for light games, 17" samsung monitor, 80 GB Seagate HD, 512 MB DDR Ram, Simple Keyboard, Optical Mouse, ATX cabinet with 300 W SMPS and a DVD Rom.