I designed and fabricated some magnesium alloy lugs at my university and assembled a fixed gear frame using carbon fiber tubes. The lugs were investment cast and the tubes joined by adhesive bonding. The finished frame weighs 1.0 kg (2.2 lbs). The project has a website at www.ideas2cycles.com for more details about the design and manufacturing process.
Most of the parts are whatever I found laying around. The bottom bracket shell has no threads so a threadless BB had to be used. The seat mast topper had to be machined from an old seat post to match the diameter of the integrated seat post. A 130 mm rear hub was welded fixed and made to 120 mm by removing spacers and dishing the wheel again.
Greetings from Finland!