To run synaptic, type this in a terminal:
$ sudo synaptic
then search for the package name, or part of it.
Or, do whatever you did to install from the .deb files (again), but just open the .deb file (rt-click, open with whatever you used) and look for something (a tab) telling you which files it put where.
To find whatever you installed, search the entire computer for them:
$ sudo find / -iname "*some-string-in-the-program-name-you-installed*"
where some-string-in-the-program-name-you-installed is part of the name of whatever you installed. (e.g. 'hund' or 'ird' for 'thunderbird' package, etc) Don't forget the *s.
Mint 16 fluxbox/Xfce, Mint 13 fluxbox/Xfce, Arch fluxbox/Xfce.