Jake,
I guess your problem is more SuSE-related than dia-related.
Are you running a vanilla SuSE installation (= you installed everything
from the SuSE CDs)?
I would try the following:
* Check the online update service. Install all the recommended packages
* If this doesn't help, please check the SuSE download pages, there seems to
be an updated dia package available under
ftp://ftp.suse.com/pub/suse/i386/supplementary/GNOME/update_for_8.0/applications/.link/dia.rpm
Steffen