To make a directed graph in Mathematica 6.0, you can use the built-in function Graph and specify the Directed option as True. For example, Graph[{1->2, 2->3}, DirectedEdges->True] will create a directed graph with two vertices and two directed edges.
Yes, you can customize the appearance of your directed graph using the VertexStyle and EdgeStyle options in the Graph function. These options allow you to change the color, size, and other properties of the vertices and edges in your graph.
You can add labels to the vertices and edges in your directed graph by using the VertexLabels and EdgeLabels options in the Graph function. These options allow you to specify the labels for each vertex and edge in your graph.
Yes, you can save your directed graph as an image in Mathematica 6.0 by using the Export function. For example, Export["graph.png", Graph[{1->2, 2->3}, DirectedEdges->True]] will save your directed graph as a PNG image named "graph.png" in your current directory.
To combine multiple directed graphs into one using ShowGraph in Mathematica 6.0, you can use the Join function to merge the graphs together and then use ShowGraph to display the combined graph. For example, ShowGraph[Join[Graph[{1->2, 2->3}, DirectedEdges->True], Graph[{4->5, 5->6}, DirectedEdges->True]]] will display a single graph with two separate directed subgraphs.