geom_path: Each group consist of only one observation. Do you need to adjust the group aesthetic?
#sampledata
d<-data.frame(expand.grid(x=letters[1:4],g=factor(1:2)),y=rnorm(8))
#Figure1a,1b,and1c.
ggplot(d,aes(x=x,y=y,colour=g))+opts(title="Figure1a")+geom_line()+geom_point()
ggplot(d,aes(