Yeah Mono is needed to use the linux version of Gigasmilies. But I wonder how can u have a .exe file of Gigasmilies for linux ?
Although U can install the windows version of Gigasmilies on linux. Also there are a wonderful wine based solution named crossover linux to install most of the windows programs in linux, but it is paid.
BTW to install using wine, follow this link for instructions
http://www.psychocats.net/ubuntu/wine and for a comprehensive guide to wine visit
http://www.winehq.org/site/docs/wine-faq/index