Sibelius says some of my fonts are missing, and it turns out when i put in a diddle it looks just like a box on the tail on the note. any idea how to fix that?

Check with the Sibelius Help Center:
http://www.sibelius.com/cgi-bin/helpcenter/search.pl?com=main

For your reference, they refer to these diddle slashes as ";tremolos."; That might help so you're speaking the same language when inquiring with them.

Thanks Jim, I found what I needed. Appreciate it.