Conflicting fonts should always be removed rather than just resolved (turning one or the other off). Especially since Font Book doesn't tell you which one it disabled. The conflicting fonts Office 2008 and Office 2011 install are very old OS 9 style TrueType fonts.
In the /Library/Fonts/Microsoft/ folder, you should remove these conflicting old TrueType fonts. Note that they do not have a file extension such as .ttf .
Andale Mono
Arial (2008)
Arial Black
Arial Narrow
Arial Rounded Bold
Comic Sans MS
Georgia
Impact
Tahoma
Trebuchet MS
All of the above are common to Office 2008 and 2011, except for Arial, which I added (2008) behind. Office 2011 installs Arial.ttf, which should not be removed as it automatically replaces the version installed by OS X.
If possible, delete the older fonts through Font Book's interface. That only because Font Book doesn't like it when you manually remove fonts. That almost always goofs up its database, and you then find you can't do things like enable or disable fonts, add new ones, or fonts that are active won't show up in all apps.
If you can't figure out which are which in Font Book's interface, then remove them manually. Fixing the issue stated above is simply a matter of starting up in Safe Mode (restart and hold down the Shift key), then restart normally. This resets Font Book's database.