Installing a .deb file can be done via the commandline tool dpkg:
dpkg -i hiawatha_6.11_i386.deb
This works for both Debian and Ubuntu (which is a Debian clone).
Installing on other OS's is done via the source tarball:
tar -xzf hiawatha-6.11.tar.gz
cd hiawatha-6.11
./configure
make
make install
Compiling from source requires several developer libraries to be installed. How this is done depends on what OS you are using. I'm not familiar with CentOS and Slackware (last time I used those is more then 5 years ago), so I can't help you with that. Use their support forums for help.