As always, it's a good idea to keep XP's font list from climbing too high into the ozone.  This is one item I haven't had to worry about... yet.  The fonts folder hasn't changed since I installed Word 2000 last fall.  I thought maybe Xara3D (a 3D-text program I installed a while ago) might add a few fonts of its own, but nope.  I'm guessing that if I used apps like Photo Shop, Paint Shop, Front Page or Dreamweaver, or added another word processor like OpenOffice or Word Perfect, then extra fonts might be an issue.  Then again, I haven't tested that theory, and have no plan to either.  Anyway, a visit to Start Menu / Control Panel / Fonts (or Start Menu / Run... / type fonts / press ENTER) will show you which fonts are installed so you can decide what stays and what goes.  Remember that some fonts (like MARLETT.TTF) are key to the good looks of Windows XP and other programs, so be careful what you delete.  Back up all the font files before doing anything else

More about Fonts in Windows:
    - How To Install or Remove a Font in Windows (Microsoft)
    - Fonts supplied with Windows XP (Microsoft)
    - Ellie's "Treasures List of Essential Fonts for Windows"
    - Sue Chastain's "Overcoming Font Overload in Windows" (About.com)
          - Part 1: Windows Font Limitations
          - Part 2: Trimming your Font Collection
          - Part 3: Windows Fonts That Should Not Be Deleted