I need to create a timeline between 2 given dates, ie:
2006-01-20 – 2009-02-14
The timeline must be drawn on a given width (can be altered), ie:
600px
But I need to add markers, one on year beginning, and others 4 times during the year (each 73 days aprox):

Any tips?
I think the axes in the Flex Charting package allow you to do such formatting by default.
If you need to do more, Flex Charts also allow you to draw of them. That might be what you’re looking for.
Link: http://livedocs.adobe.com/flex/3/html/help.html?content=charts_formatting_02.html
You could of course, always do it from scratch yourself if you wanted, but the amount of time you spend on that might not offset the price of the professional edition (To get the charting component, unless you have that already).