KOffice 1.4 had OD supported added on during its lifecycle. The current version is 1.5 and this is the one with ODF built in.
See
http://www.koffice.org/news.php
This is available in Debian Unstable so the apt-get it you will need to point to Unstable - which may have consquences on your total installation.
Alternatively get it separately from the KDE site.
Either way you could have some problems because of dependencies so if you want to remain in Testing I'd suggest you wait till Koffice 1.5 is moved to testing.