Linear least squares fit with errors in both x and y values.

Hi,
I'd like to perform a weighted linear least squares fit with R on data
with varying errors on both vectors. I can do this with one axis using
lm, but have no idea where to go from here. I've tried googling, but no
idea. Any suggestions?

I'm also trying to plot these errors on a graph. Again I can see how to
do it for one set of data but not the other.

Thanks,
James