The problem £100 is a false economy in many ways. Once it gets reviewed in a PC Mag it'd likely be slated for non-upgradability least to say the build quality issues. And even IF you managed to procude something near decent, where's your profit margin!?
And things have changed massively over the last 5 years. If you could do this 5 years ago you'd be minted (my first proper machine was a P133 for around 850, the only machine (base unit only) for £100 was a 386), nowadays relatively the costs of PC's have fallen to a level that £100 PC's are pointless in UK.
People are spending over £100 on IPODS! let alone computers.
Even the most hard up people I know still want a TFT monitor when they're looking for a PC. Even second hand I find it hard to source 15" SECOND HAND TFT's for under £35. Add £18 for case, keyboard, mouse and speakers you're left with £48 for components.
"puts dragon's den hat on" it's not a business my friend. Maybe you should think about joining the company that makes the $100 (well at the moment over that) laptop for DEVELOPING countries?!