While much of the green computer focus worldwide is on laptops, UK companies are doing interesting things with desktops.
Aleutia offers low-power units that "are designed to easily connect to solar power and work in remote places." Case studies include Africa and Central Asia.
VeryPC promotes its Broadleaf desktop as "categorised as ‘Class Leader’ by DEFRA Quick Wins", "BFR, PVC and halogen free in line with ECMA-370, the environmental standard", "the only desktop PC to be endorsed by the Energy Saving Trust Recommended scheme". (More about Green ICT product standards in Europe.)
Here's a guide to go about finding the greenest e-gear. It's not as easy as it sounds!