If you are wondering where this disappeared in Excel 2010, you can blame the Ribbon. The Ribbon is designed to show the menus with commands to help complete a task. As such, there are the basic commands on each tab, and then there are the Contextual tabs that pop up only if an object is selected.
The Drawing tab is one such contextual tab. It will pop up whenever a drawing object is selected (such as a line, box, image etc.). Which is all fine, but where do you start drawing a line if the Drawing tab does not show up unless you have a line?!
To get your initial obect to use the Drawing tab on, you have to first go to the Insert tab, then select Shapes and pick your shape, then draw it on the worksheet. Now you will see the Drawing tab (as it is a contextual tab), appear in a different color.