Sounds like you are talking about the icons in the start menu.
If so, you have a couple of choices:
1 - create a new icon on the desktop by right-clicking desktop > New > Shortcut > browse to the office program executible > after creating the shortcut, right-click it and use the change icon function.
Note - you can use either Icon Packager|Settings to remove the overlay arrow if you are running a theme, or you can use TweakUI (download from Microsoft) - which has the option to assign "none" to the shortcut arrow - if you do not want the arrow overlay.
2 - create a shortcut in "C:\Documents and Settings\All Users\Start Menu" for the office programs you want, using the method in #1 to assign the image you want displayed.
Note - you can move the default start menu icons to a holding folder for future replacement.