I miss the dialog box and the quick switch to search and replace. Fortunately, it is still there (as advanced Search).
Here is how to recreate the old default Key Shortcut:
Open up System Preferences » Keyboard » Keyboard Shortcuts. Select the tab for Application Shortcuts, and click the plus sign to add a new entry for Microsoft Word. To choose Word, you'll first have to select 'Others' and Navigate to the MS Office Folder.
As the Menu Title enter Advanced Find and Replace... to match what the menu item is called.
As the shortcut enter Command+F.
Now, add another entry for Word and as the Menu Title enter Find... and as a shortcut enter something that is not used elsewhere. I chose Command+Control+Option+Shift+F.
[crarko adds: I haven't tested this one. Just be sure that the Menu Title entry is identical to what the menu item is named in Word.]

