Here is the best way, for me, to add code inside word:

1. Go to Insert tab, Text section, click Object button (it's on the right)
2. Choose OpenDocument Text which will open a new embedded word document
3. Copy and paste your code from Visual Studio / Eclipse inside this embedded word page
4. Save and close

Advantages

The result looks very nice. Here are the advantages of this method:

• The code keeps its original layout and colors
• The code is separated from the rest of the document, as if it was a picture or a chart
• Spelling errors won't be highlighted in the code (this is cool !)

And it takes only few seconds.

Download and install Notepad++ and do the following:

1. Paste your code in the window;

2. Select the programming language from the language menu;

3. Select the text to copy;

4. Right click and select Plugin commands -> Copy Text with Syntax Highlighting;

5. Paste it into MS Word and you are good to go!

Update 29/06/2013:

Notepad++ has a plugin called "NppExport" (comes pre-installed) that allows you to copy to RTF, HTML and ALL. It permits dozens of languages, whereas the aforementioned IDEs are limited to a handful each (without other plug-ins).

I use Copy all formats to clipboard and "paste as HTML" in MS word.