Step 17: Add component symbols
pstoedit -f fig inputfile.ps outputfile.fig
It is possible to generate a schematic format output file, but I found this hard to add components to.
Use Dia to open the .fig file you just made. Dia is a great little program which has an excellent range of objects which can be snapped to lines, a bit like MS Autoshapes, only much better. If you have used Visio, you should be comfortable with Dia. Choose the "Circuit" category of shapes. Using the image of the components as a guide, snap in symbols to replace them. Visit the Dia website for extra symbols in the "Electronic" and "Circuit 2" categories. (Others may exist, I just haven't found them)
I used the lamp symbol to represent unknown connections - ie those which are connected to a "free" hole on the solder side. These can later be filled with corresponding colours.
Dia has a text tool. If you snap text to a shape, it will move with the shape. You can also attach it to lines where you see a connection point. You probably want to add values and/or identifiers this way.
You can also create new symbols using Dia. Create the symbol as a diagram, then export it as a .shape file. The files are easily editable in a text editor to remove surplus connection points and tweak line positions.
The majority of datasheets for chips and transistors can be found on the internet, though you may have to dig somewhat. Create "mystery box" symbols for any mystery devices. You may be able to work out what they are once you have rearranged the drawing into a schematic.