[R] Plotting multiple lines

[K Skanes]

Hi,

I have a data set with 7 years worth of data, and 2 different values (a real 
value and a model value) of interest in each year for different lengths.  I 
would like a plot with the year on the y axis and an animal length along the 
x axis.  For each year I would like to see two lines, one representing real 
data and one representing model data.  I would like either the model or real 
line to be red.

I have no idea how to start this.  Can anybody help me??  If I didn't 
explain it well enough, I can try to explain it better...

Thank you,
Kay