Scatter plot with median and interquartile lines

[ninja-lewis]

I'm trying to plot house prices and house types on a scatter plot in
Excel. To aid analysis by the reader I want to include median and
interquartile lines for each category like 'this example'
(http://img.photobucket.com/albums/v418/ninja-lewis/chart.gif).

I can plot plain scatter plots no problem in Excel 2003 but I don't
know where to begin for adding these extra features. Can anyone help
me?

ninja-lewis