Good news! I'm glad that was all you needed in order to solve the keyboard layout problem. If you will send me a private message and tell me what type of keyboard you have (e.g., 105-key generic PC - US, AZERTY, etc.), I think I can send you a PDF file of Polytonic Greek / Spanish keyboard layouts for that keyboard type. (There is a way to do this in Gnome but not in Xfce, AFAIK).
Now that you know about Synaptic, you can install other applications and try them out -- assuming that you have enough spare space in your root (/) partition. The great thing about a Linux distro's designated repository is that you can be certain that the software therein will work with your distro, and also that is "safe," i.e., no worries about viruses, malware, or spyware.
One thing to be mindful of is that although you have an Xfce base/core system, it is possible to install Gnome and/or KDE applications if you wish. (You could, for instance, install Evolution [for e-mail and calendaring], Okular [a PDF reader] or K3b [a CD/DVD burning app]. However, the "look and feel" of the program(s) might be slightly odd). Synaptic will pull in whatever Gnome or KDE-based dependencies a particular program needs to work and will install them; some applications will require lots
of extra dependencies. So it is always a good idea to check this in Synaptic -- carefully review what will be installed before you press that "Apply" button for a second time and commit yourself.
The default apps in the Mint Xfce Community Edition are well chosen, in my opinion, but you might consider exploring some other Xfce applications. For a basic list, you can take a look at this thread from the PCLinuxOS User Forum:http://www.pclinuxos.com/forum/index.php/topic,79047.0.html
." 4 Sept. 2010