excel 2000 only ...

Technically, it's the easter egg for the Microsoft Web Components, but you access it from an Excel workbook saved as an interactive web page. Requires Excel 2000, the Microsoft Web components, and DirectX.

Open a new Excel workbook.
Select File * Save as Web Page
In the Save As dialog, select 'Publish Sheet' and 'Add Interactivity'
Save to an htm file on your hard drive (any file name).
Open the htm file with Internet Explorer 5.
Select cell WC2000 and scroll the sheet such that cell WC2000 is the first cell on the left. Highlight the entire row.
Press Shift+Crtl+Alt and click the Office logo in the upper-left.
Your screen will be transformed into an auto racing game, with developer credits (and other things) visible on the roadway. Use the following keys:

Arrow keys: to steer and accelerate
Space bar: To fire at other cars
O: To drop an oil slicks
H: To turn on your headlights