Could I just draw your attention to the first part of Rojashs post
Word should show the list of fonts installed on your computer (i.e. the fonts are not unique to Word, but are available to every application)
i.e. it's not a word problem so you can't fix it in word!
you can fix it and not download anything, reinstall windows!
Or if you can force yourself to download an extra for windows actually from microsoft then tweakUI can fix it easily too.
http://download.microsoft.com/download/f/c/a/f ca6767b-9ed9-45a6-b352-839afb2a2679/TweakUiPow ertoySetup.exe
Once you install it click Start > Settings > Control Panel, double-click the new TweakUI icon, go to the Repair tab, select Repair Font Folder from the drop-down list and then click Repair Now