MegaGlests' game mods menu let's you install many new mods. Even more are available on the MegaGlest Wiki and the Mods forum.
I don't think that dll files can be used in Linux but if you still wanted to use them there should be an option with your compiler or IDE to compile as a dynamic link library (DLL). There are tutorials at Code Project. For more information about dynamic libraries on Linux check out YoLinux.