.deb file is simply a zipped and tarred file, like a
.tar.gz, so you can use
tar to unzip it. Grab the
.deb you want to install, go into a directory into which you want it expanded, and simply
tar xf /path/to/package.deb. You will then see three files:
debian-binary, which contains (I believe) a deb version number,
control.tar.gz, which contains metadata and install/uninstall scripts, and
data.tar.gz, which contains the actual files. To extract the files, run
mkdir root; tar Cxf root data.tar.gz and you will have a directory structure in
./root that mirrors the structure where the files would be installed in the actual file system. You can find the file you're looking for there.
If you want the entire package installed, I very strongly suggest you use
dpkg to actually install it (
sudo dpkg -i /path/to/package.deb), as it will automatically run the pre- and post-install scripts if needed, keep track of what's installed where, and allow you to uninstall it cleanly and easily. But if you really feel the need to bypass all package managers, you can use
sudo tar Cxf / data.tar.gz to extract the files into the root directory tree, which should place everything where it is meant to go. But do run or at least check for
postinst scripts in the
control.tar.gz archive to see if you need to do anything important before or after installing.