Hi. I have followed the instructions on my N900 and I get this:

home/user/MyDocs # dpkg -i oracle.deb whatsapp.deb
(Reading database ... 23274 files and directories currently installed.)
Preparing to replace oracle-embedded-jre 1.6.0u30 (using oracle.deb) ...
Unpacking replacement oracle-embedded-jre ...
dpkg-deb: `whatsapp.deb' is not a debian format archive
dpkg: error processing whatsapp.deb (--install):
subprocess dpkg-deb --control returned error exit status 2
Setting up oracle-embedded-jre (1.6.0u30) ...
Errors were encountered while processing:
whatsapp.deb