When my character equips a greatsword or any two-handed weapon, equipped cloaks start "lagging" and floating off the shoulders. I've tried messing around with the graphics settings and nothing happened; if I go back to one-handed weapons, everything's fine again.

It's exactly like this clip here: http://youtu.be/_8HwLtE-t-E

I can't seem to find a solution, so any insight would be appreciated - I just played the OC without a cloak, but in MOTB it seems all my armors now have cloaks by default and it's incredibly irritating...

Well, you could make cloaks invisible and see what that does. Should allow you to use cloaks, but the visual presence of them will be removed.

http://social.bioware.com/forum/Neverwinter-Nights-1/NwN-1-Technical-Support-Self-help-for-all-versions-and-expansions/NWN-MASSIVE-FPS-drop-when-RobesCloaksRanged-Weapons-are-seen-4541153-1.html

The folks in this thread discuss various ways to do it.

These overrides could also be tried. I used one of these myself way back when, but can't remember which:
http://nwvault.ign.com/View.php?view=Other.Detail&id=1131
http://nwvault.ign.com/View.php?view=hakpaks.detail&id=6934

Cloaks were an after-thought and came out in a patch at some point. You could always equip them, but not always see them. Once they were added, there were problems with them for some folks.

I've never heard of a good solution, but you may have luck with the community patch 1.70 or playing w/ graphics settings. Good luck!

Uh... this is in reference to NWN2, not NWN1.

Does it help to remove the cloak/armor and re-equip it? I know this used to work for some glitches in NWN1.

Woops, sorry about that. I never had cloak issues personally with NWN2.

Since you've already tried adjusting in-game graphical settings, I'd consider heading into your graphics card controls and seeing what can be done. What brand of GPU are you using?

The only other thing that comes to mind is opening up the .ini files and attempting some tweaks there. If you web search nwn2 (or the full name) ini tweaks you should come up with some recommendations. One other random thought would be to look up some cloak mods on the NWVault. It's a longshot, but one of them may have the side effect of fixing the problem.