So here's the problem, I haven't played NWN for a long time but I seem to remember a mod from nwn vault that made the helms invisible, the problem is I can't seem to find the mod, and IGN closed the website... Is there a way to hide helmets?

Edit: Maybe I'm confused and maybe the mod was for NWN2... Either way my sorceress looks ridiculous with a helmet on...

A helm in NWN is a replacement head, so there is no way to 'hide' them -- they are not separate items. However, there is a trick that you can perform to fool the engine into hiding them: place your armour and helm in the quickbar and unequip both. Now, quickly equip your armour first, then the helm. If you do it correctly both will be equipped but the engine will not have time to display the helm. Magic!

I believe that technically only works for yourself, in multiplayer won't other players still see your helm? Not 100% sure on that but given that it's a local rendering issue (I think) then that would seem to be the case...

Yes, it's only a local rendering thing. But not liking helmets is also a personal thing, so multiplayer is a non-issue.

Actually it is an issue for MP, at least for me, I want my friends to have the same feedback(visual and all) I have.

I decided to just not use head gear, just like I refused to multi-class because it's, most of the time, stupid, I don't like metagaming much, and actually think that in most cases multi-classing is ridiculous(One thing I think D&D4E did well was fixing the need to multiclass in order to be useful).

The Customize Character Override Hak might do the trick. I used it in my play through to change the color of my cloaks, but it looks to have options for everything.

It says "Works in multiplayer if installed on the server". (I know nothing about that)

That's a great override, but it doesn't let you hide helmets. Just change their appearance. (as explained above, there's no real way to hide helmets in this game.) It does let you hide cloaks, if you hate those.

The override also won't work in multiplayer unless you're the guy hosting the game. Which you probably aren't.

Honestly, for sorcerers and wizards I just swallow the lack of the helmet slot and go bare-headed. Looking like a proper wizard is more important than getting that last +2 CHA or something.
(and in single player I might 'cheat' by using the toolset to add the helmet properties to some other item if I really need them. But that won't work in multiplayer, unless you have a DM who's feeling nice. Or unless you're hosting the game. Then you can just go in the toolset and change the helmets into some other kind of item.)