Unfortunately you can not break up the formatting on a trend line like you
can a normal series. To get around this limitation, plot a second series
that reflects your trendline. You can use the TREND and/or FORECAST
functions to build the new trendline. Once the trendline is available as a
second series, you can apply individual formatting to the points and series
as you would with any other chart series.

Although this example contains a lot more than you need, the basic concept
of adding the trend as an additional series is described he

http://www.pdbook.com/index.php/exce..._linear_trend/

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Regards,
John Mansfield
http://www.pdbook.com

"odcltd" wrote:

I have an Excel chart, a line graph with 10 data sets charted on it. The
time scale is 2000 to 2007 and I'd like the forecast data, i.e. 2005 to 2007
to be dotted.

Therefore the line should be solid to 2004, then dotted thereafter. Is
there an easy way to create such a line?

I'm using Office Excel 2003 v11.5