$ dpkg -L maemotex | grep bibtex
/usr/local/maemotex/070802/bin/armel-maemo/bibtex

to make it easier to find, try
$ root
(or however you have set up to gainroot)
$ ln -s /usr/local/maemotex/070802/bin/armel-maemo/bibtex /usr/bin/bibtex

after which you should be able to just do
$ bibtex <filename>