Thanks to Mohammed Hassan now I know an alternative (alternative to the official howto) way to generate a .deb package for Maemo.
If the package already exist in the Debian repositories, you can get the
.dsc file (for example in an ftp like this:
http://ftp.debian.org/debian/pool/non-free/s/spim/ ) and execute the
dget -x DSC_FILE_URL
It will download the package and will unpack it in the current folder. You have to enter in the created folder and edit the debian/* files to personalize settings, mantainer data, add deps ecc...
When you're done, you can generate the package with the usual command: