Looking for a statistic for custom built PC's.

[CSammy]

We all know companies like ASUS, Gigabyte, MSI, DFI all profit off people who like to custom build/upgrade their PC's.

I'm looking for a reliable statistic that breaks down the home PC industry into those that are OEM (like Dell, Gateway, HP etc...) to those that are custom built.

Would anyone have an appropriate link, or something to point me in the right direction?

Thanks