The Word plug-in formats the citations in your “Default font”.

To change this (in Word 2003), under 'Format' and then 'Font', there is a button on the bottom of the window called 'Default'.

Prior to clicking the button, select the font and the size you want all text to appear, and then click the 'Default' button, and lick 'yes' to confirm. This is now the standard for all new text, including Zotero citations and bibliography.

If you use formatting styles, Zotero citations will show up in the default style (usually 'Normal').