Hi,
Unzip the hud and move it to your "tremulous/base/ui" folder (for easy uninstallation). Depending on the hud, there can be a "install script". If there is, you would go into the console and type /exec ui/something_install.cfg (replace something with whatever).
If there isn't, you would have to look at the files, and then under "/cg_hudfiles" you would put the appropriate file. For Example "/cg_hudfiles hellrider.cfg" This is just using Hellrider's huds. Other huds will have different configuration. Just look for something like this.
{
loadMenu { "ui/hellrider-v1.1-alien_builder_hud.menu" }
loadMenu { "ui/hellrider-v1.1-alien_general_hud.menu" }
loadMenu { "ui/hellrider-v1.1-human_hud.menu" }
loadmenu { "ui/hellrider-v1.1-tremulous_default_hud.menu" }
loadMenu { "ui/teamscore.menu" }
loadMenu { "ui/hellrider-v1.1-loading.menu" }
}
(ui_menufiles is for the non-ingame display. For example, the main menu.)