[R] igraph and tkgraph

[Tom Backer Johnsen]

I have a number of (directed) graphs based on social groups, where the 
members have expresed likes and dislikes in respect to the other 
members.  tkgraph makes it simple to draw the graphs in a very pleasing 
way, but I would like to differentiate between positive and negative 
relations in the graph by having the edges for the negative relations 
dashed and the positive ones continuous.

Is that possible?  If so how?

Tom