Looking to to buy a PC with a complete custom configuration

Do you know of any PC vendors that you could recommend who will allow you to buy a PC built by them that is custom-configured from the ground up? For example, if you wanted everything possible to customizable, from which OS is pre-installed (with recovery CD/DVD option), to the type of motherboard, processor, case color, even motherboard support for certain legacy hardware such as ISA slots? Thank you