overlay scatterplot - multiple best fit lines.... how?

[CedricC...@gmail.com]

I want to be able to plot a best fit line for EACH of the pair of Y-X
variables chosen for the overlay scatterplot. I would like therefore 3
best fit lines to appear in the final scatterplot. I intend to plot:

Y - X Pairs
Observed - Year
Predicted - Year
Forecast - Year

The Observed, predicted and forecast variables are three different
numeric variables.
Predicted is the result of a linear regression
Forecast is a computed variable using the regression constants for YEAR
cases that are not included in the other 2 variables.

Any help will be appreciated. :)

tnx in advance