What GPU-APU configuration should I buy for mining Bitcoins? I want to make own computer for mining bitcoins. I read a lot of it but I have some questions. I want to buy APU + Graphic card and I am wondering when I my computer is mining is using for that CPU + GPU(from APU) + normal GPU. 

Can you tell me if this configurations is good?

Gigabyte GA-990FXA-D3 s.AM3+
ATI RADEON HD 5870
A8-3870K 
DDR3 2GB CL9 1600Mhz

I will be running this on linux.

Every two months I will be adding one more ATI GPU until I get 4 of them. Is that good strategy?
It's essentially too late to be worthwhile GPU mining because FPGA's are much more energy efficient, and cheaper to buy per unit of output. This has meant the difficulty has risen high enough that you won't cover the cost of your electricity (or your hardware) with GPUs. ASICs are likely to be shipped soon, which will largely make FPGA's obsolete. You can pre order ASICs from multiple manufacturers; Butterfly Labs is one.