How come you don't like Squirrelmail? (if you don't mind me asking)
Anyways, if you have SSH access, I don't see any reason why you shouldn't be able to setup horde. I have never used it, but I suggest downloading it, and reading the documents. You should just have to download the archived file, extract it, and then edit the config files. That's the way squirrelmail works, so horde probably would to (but again, never used it so i really don't know). Just read the documentation and install file.