An ultrafast x-ray detector system is under development at Lawrence Berkeley National Laboratory (LBNL) for application primarily to studyies of ultrafast magnetization dynamics. The system consists of a fs laser, an x-ray streak camera and an ellipitically polarization undulator (EPU) beamline. Polarized x-rays from an EPU can be used to measure x-ray magnetic circular dichroism (XMCD) of a sample. XMCD has the unique ability to independently measure orbit and spin magnetization with sub-monolayer sensitivity and element specificity. The streak camera has simultaneously a sub-picosecond temporal resolution and a high spatial resolution. The combination of the streak camera and EPU allows us to study the transfer of angular momentum from spin to orbit to the lattice in the sample on an ultrafast time scale. We describe here the performance of the ultrafast detector, the laser and the x-ray synchronization system. The observation of the demagnetization process of different samples demonstrates the ability of the apparatus.