It happened to me in Vista after a bad adobe update. Luckily in Vista, you just right click the font folder -> previous versions and it shows you which font files are missing/corrupted and you just restore them.
In your case you will need to determine which font is missing (probably all your arial fonts) and extract them from the XP cd (using the extract command from the command line) or copy the font folder from another XP system.
I got ahold of the fonts folder from another XP machine, but whenever I try to copy the files over, for all the arial fonts and a few others I get "Access Denied". I've tried from the Windows 'Explorer', from safe mode with command prompt, and from the recovery console. Any more ideas?