Could it be this simple? It worked for me!
http://forums.techarena.in/vista-help/1189255.htm
The Windows Font folder itself is using the font, hence why you can't delete the font - i.e. the very tool you're using to delete the font is using said font and thus locking the file!
When in the Fonts folder click:
Organize > Layout > Untick 'Details pane' > Now try deleting the font.
Worked a treat for me.
Seriously needs addressing in the next service pack.