Indeed, priests cannot learn more spells by scribing them. They innately learn spells as they grow more experienced, or perhaps their gods grant them powers, whatever. High or low intelligence does not affect a priest's divine abilities.
As for those two spells you mentioned, Entangle is a level 1 Druid spell and Wall of Moonlight is a level 4 Druid spell. If your priest is a Cleric and not a Druid, you will never be able to use these spells. I think in Baldur's Gate Entangle is available to both Druids and Clerics, but not so in IWD. However, if you priest is actually a Druid and can't use these spells, then you got yourself a problem
