AstralWanderer: The NWN1 expansions Shadows of Undrentide and Hordes of the Underdark are separate from the main campaign (though several NPCs from the OC do re-appear in Hordes).

Hordes does follow on from Shadows but there is a gap in the story between them (several bridge modules provide a transition adventure - one of them, the Shadow Queen also has a sequel Pawns of Darkness that takes place after Hordes).

You can of course take a character through the original campaign and then the expansions, but he/she would be grossly overpowered for Shadows. All the campaigns are worth playing in my view - NWN1's original campaign is the weakest overall, though it has its good parts.

CranGrape: Thanks, would it be ok then to create a new character for each campaign/module? I tend to get bored playing the same class/race for so long.

Darvin: Yes; the OC and SoU both presume you're beginning at at 1st level so this is exactly how it's meant to be played. In HotU the game presumes you're beginning around the 14th level, so you'll need to promote your character to an appropriate level (console commands will work). You won't need to worry about gear, though.