Could i build a mining rig with these parts? I have researched bitcoin mining for a while, and i have decided that i want to build a dedicated miner. Since i am very low on budget, I thought that maybe i could use an old computer that i have in my house for the motherboard and CPU requirements, and by only a GPU. My old computer has an AsusTek computer inc P5S800-VM motherboard, featuring an Intel Pentium 4 processor. Link:
http://www.asus.com/Motherboard/P5S800VM/

Is there a way to add an ATI GPU to this system and make it work as a miner? Thanks for any responses, and sorry if i was not clear enough - i am quite new to this field.
I have to say you did not research Bitcoin mining enough. Mining on a GPU is obsolete, reports say ASIC-based mining devices with x40 the performance have already started shipping.