According to the game's demo movie, the first pressing of the game included a soundtrack CD.
It was apparently resold at Comiket 71, so on file sharing sites you'll find that as the release date. The game's release predates that by almost two years.
Couldn't find anything definitive on the title, but "D'ERLANGER -誘惑の淫魔病棟- SOUND TRACK" seems most common. There's also "D'ERLANGER ～誘惑の淫魔病棟～ 初回特典 Main theme&BGM SOUND TRACK."
No clue on the BGM composer, but
Lip on Hip's works list says that JUNK wrote the opening and ending themes.
Alchemy SOUND Vocal Collection confirms the artists and title of the ending theme.
BY THE WAY, I strongly discourage anyone from researching this game just a heads up why am I even adding this album