Maybe I'm just dumb, but when I tried to apply the "Default Paragraph Font" to my body text paragraphs in Word 2000, the style didn't change. I tried it again, but still no good.
The Default Paragraph Font item in the Style drop-down list and Style dialog box looks like a style, but in fact it's not: what it actually does is remove any additional formatting that has been applied to the paragraph so that it matches the current style definition. (You might also say that it simply reapplies the current style to the paragraph.)
Press Ctrl+Spacebar to restore the font formatting of a selection to the style's default font formatting. Press Ctrl+Q to restore the paragraph formatting of a selection to the style's paragraph formatting.
Bypass the Styles and Formatting Task Pane
The new task pane for styles in Word 2003 and Word XP is difficult to use, especially if you want to change the attributes of a large number of styles at the same time. The extra styles added when you bold a word become confusing. I think Word calls these "formats," but they appear in the same list.
You can bypass the Styles and Formatting pane if you want. Choose Tools » Customize, click the Commands tab, and verify that the correct template (for example, Normal.dot) is selected in the "Save in" drop-down list. Click Format in the Categories list, then drag the Style... item (the one with the ellipsis after it, not the Style drop-down list) to a menu or toolbar. You can then go directly to the Style dialog box.