For some reason when I installed OpenOffice 3 this week in Ubuntu, it didn’t actually update the icons from 2.4. I looked all over my icons folders, and couldn’t find them. So I have put together an icon set of the official icons plus some Office 2007 icons for the .doc, .xls, and .ppt files.
You can download it here: OOO3_icons.zip
It’s a Gnome icon theme, but you’ll need to do a few things to get it working how you want. Extract the folder into your /home/you/.icons directory, and open the index.theme file with a text editor like Gedit or Nano. Replace the names in the Inherits line with the name of the icon theme that you normally use. That way, it will use these icons for OpenOffice, but fallback to the theme you entered on that line for the rest of the icons.
Once you’ve done that, open your Appearances control panel, hit the customize theme button, and switch your icons to the ones you just installed.
The change should take place instantly, but if it doesn’t, try logging off and back on.