The material in the disk will form the planets. Because there is a temperature gradient in radial direction with the highest temperature close to the center of the disk and decreasing towards the edge, only silicates and other rocky materials will be in their solid state close to the center of the disk. Further out, water ice, amonic ice, etc. will also be solid. Dust grains will start sticking together forming larger and larger rocks. The outer planets are large enough and the temperature at the distance from the Sun is cool enough so that they could accrete gas from the cloud out of which the solar system was formed.
Comets consist mainly of ices.
The are thought to reside in a spherical cloud far beyond the orbit of Pluto called the Oort cloud. They are pulled into the inner solar system by gravitational resonances between the outer planets. Last October, the first planet orbiting a solar type star was discovered around 51 Pegasus. Since then, half a dozen other planet detections have been made. This method is the most sensitive to large planets with small orbital radii.