No problem. That's why everyone is here.
In your workbook, hit ALT+F11. That will launch the Visual Basic Editor.
In the left hand pane (that's the Project Explorer), you'll see VBAProject(YourFileName.xls). When you expand it you'll see a folder named Microsoft Excel Objects. Open it and double click on the sheet where you want the rows entered. If none of that is visible, then hit CTRL+R to open the Explorer.
A blank window will open on the right-hand side. Paste the code that I posted in there and hit ALT+Q to return to Excel.
Now change/enter something in column D and see what happens.
The best way to learn this stuff is to start playing with the macro recorder. When you record, VBA will create a folder called Modules. In each instance of Excel, when you record macros, VBA will put them in successive modules. Module1, Module2, etc.
Just note that the recorder records literally every move that you make so you'll wind up with a lot of unnecessary code that will need to be cleaned for performance.
Post back with more questions!
Smitty
EDIT: here's a website that will give you an introduction to Excel VBA. It's a pretty good tutorial.
http://maths.sci.shu.ac.uk/units/ioa/