2-3? Try 4 songs are cover songs:
* Babe I'm Gonna Leave You = Joan Baez, a song that Zeppelin originally gave no writing credit to Joan (later updated to give credit)
* Dazed and Confused = Jack Holmes wrote and recorded it a couple yrs before Zeppelin. Also, the Yardbirds did this song (at least live) before Zeppelin. Again, another case of Zeppelin taking a song and not giving credit until years later
* You Shook Me - Willie Dixon
* I Can't Quit You Baby - Willie Dixon
the other 5 tracks were originals. On that note, of the 4 songs that were covers, those 4 covers took up over 24 minutes on the album while the original songs took up just over 20 minutes. So, technically, over half of that album is a 'cover album'.
now, don't get me wrong, I'm not saying they suck because of it. I think Zeppelin's first album is probably their second best album (after LZ II), but it IS a cover album to a large degree.