Plotting fitted values vs observed ones in R or winbugs

Question

I want to plot the fitted values versus the observed ones and want to put straight line showing the goodness of fit. However, I do not want to use abline() because I did not calculate the fitted values using lm command as my I used a model that R does not cover. I calculated the coefficients and used them to calculate the fitted values. So, what can I do to obtain such a plot in R or in winbugs?

Here is what I want

Answer 1

Still no data provided, but maybe this simple example using the curve function will inform the process:

x <- 1:10
y <- 2+ 3*(1:10) + rnorm(10)
plot(1:10, y)
curve( 2+3*x, 0, 10,  add=TRUE)

Note to new R users. the expression y_i = 1 - xbeta + delta_i + e_i would fail in R in part because the x and beta are not separated by an operator. But if you do understand R's matrix syntax it might be a very compact expression even if "X" were multidimensional. All of htis depends on the specifics which we are so far lacking.