Recent Word versions do allow you, at Tools|Options, Spelling and Grammar tab, to put a check mark at "Ignore words in UPPERCASE." A check in this box will let the spellcheck pass on most acronyms.

Of course if you have the option to "Correct two Init Caps" set in Tools|Autocorrect Options, (which is handy if you have a tendency to not notice when CapsLock gets left on) an acronym at the beginning of a sentence will probably get changed to not all uppercase and could still get spellchecked.

John