Dynamic chart (moving in time)

I am strugling to find the most efficient way to create a chart I need. It is supposed to be a forecasting tool and I want the chart to change as time goes by.

As an example: We are now in May. Let's say I have actual sales data for Febryary, March and April, in addition I have forecasts for May and the following eight months (12 months total). As May is coming to an end I will soon have actual data for May as well. The actual as well as the forcast data will be manualy registered, but what I want is a chart showing me the three months prior to the current month of actual sales data, plus the current month and the following eight of forecasts. How can I make the chart work in such a way that it will change to always stay updated with three months of actual sales data (prior to current month) and nine months of forecasts (current + eight future months)?

To exemplify further:
If the month is May 2012 i want the chart to show:
February 2012 - January 2013; February - April actual sales; May - January forecast sales.

If the month is June 2012 i want the chart to show:
March 2012 - February 2013; March - May actual sales; June - February forecast sales.

etc. etc. etc., and I want this change in the chart to happen automatically, of course, given that the input data of actual and forecasts have been entered.

Is there a way to do this without involving VBA programming?

Thanks in advance!