I'm talking to Arngeir in order to learn where the word walls are. I've done several now. I'm just wondering though... if these are dungeons with specific quests (like the Bard's College quest), am I screwing myself out of doing them later?

You may like myself come across items relevant to the Bards college, pick them up Beth had the foresight to equip dialog options and quest shortcuts in some cases for those items so that you can complete them. certain barrows/ruins are however locked and you cannot enter them until the relevant Guild quest is taking place, some that come to mind are Sarthaal for COW and the Dustmans Cairn (rough remembered name) for the Companions

The dungeons will respawn and major quest-related dungeons like Labrynthian have a special trick to keep you from completing it early.

So doing the world walls shouldn't be a problem.

Many thanks.

Saarthal, Dustmans Cairn, Labyrinthian, and Korvanjund(spelling?) are all locked off for faction quests. Either completely, or by a collapsed passage that only opens if oyu have the quest in question.