In the Yahoo interactive chart (for DJI), I couldn't get a weekly chart and a 40-week ma.

Step by step:

-- Go to http://finance.yahoo.com/echarts?s=^DJI
-- Click on "Full Screen" to get a bigger chart
-- Click the reset button
-- Change the date in the "FROM:" box to be 10 years ago (defaults to weekly data)
-- Click "Technical Indicators" drop-down box, choose "Simple Moving Average"
-- On pop-up, enter 50 for the time period and click "draw"
-- Click on "Chart Settings" to customize as desired. I use candlesticks and logarithmic.

Unfortunately, Yahoo settings for a saved date range don't work. However, if you go here:

http://finance.yahoo.com/charts?s=^DJI#chart10:symbol=^DJI;r...

...all you need to do is set the "FROM:" date. For some reason, the "From:" date isn't set properly via the URL -- it defaults to a single day chart. I think because the URL processing expects one of the push button values, so it ignores any entered values. A Yahoo problem, which I've noted to them via their feedback form.