I have Microsoft Office installed and am also running OS X 10.6.5. All I can tell you is that MS Word does NOT interfere with Filemaker. The only difference is I have MS Office 2008. Have you changed the ability to enter these fields in Browse Mode? Even if you haven't, you should check the Inspector for this setting.
And you can't edit summary or calculation fields, so you should check these fields in Manage | Database | Fields to confirm that they are data fields such as text, date or number...