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 *www.psychocats.net/ubuntu/wine and for a comprehensive guide to wine visit *www.winehq.org/site/docs/wine-faq/index