Just downloaded DF yesterday night, played it today and have gotten the basics.

Anyways, I joined the Mages Guild and took a quest about taking some spider venom or something in a place. I went to the place and found some loot on the floor just 2-3 rooms in the place, and believe it or not I found some spider venom there! So I immediately get myself back to the Mages Guild and try to hand in the quest.
I could either press "Talk" or "Take Quest" (or something). When I pressed Talk all I got was a "Just because we both are in the Mages Guild doesnt mean I have to help you", I then pressed "Take Quest" and got something like "No response". Tried "Talk" again and got the same reaction as from "Take Quest"...

So, easily said:
It doesnt work.

What have I done wrong? Is there a specific "piece" of spider venom that I have to find which is a whole lot farer in the place?

Tell me that you have a save BEFORE leaving the dungeon...?

Your last sentence addresses the issue correctly: believeit or not, t here are specific quest items that have the same lame description as ordinary items. In other words, by coincidence you found one of those, which is NOT object of your mission.

You will get a spécific message when you find the right component. And my guess is, you have to kill a spider or something venomous for that and check its inventory.
Please take some time reading this:

http://www.uesp.net/wiki/Daggerfall:Quests

Look up the Mages Guild part. I guess it is something like Grab / Retrieve and Ingredient.

The same rationale applies to other MG quests (ie, doing the Open Spell quest requires you to cast the standard Open Spell you buy in the MG, not going to Spellmaker and make one).

EDIT: Because I find this approach to quests svcky, I ONLY do two kinds of quests for MG: the Guard the Guild Item and the Defend the Mage in Trance, which you always do inside the guild. Quick and safe....

The ingredient for a MG quest will always be found as a lone item on the floor or a table (except for mummy wrappings which are on a mummy).

The quest item will show up in your inventory on a GREEN background.

But there is also a specific message that pops up when the dude finds the thing, yesn't? Just to make sure...

Yes, unless there's a glitch.

(I did a Fighter's Guild quest not long ago called "Fighters Lich". Trouble was, I killed all the Liches in the dungeon and never got a pop-up message. However, when I went back to the quest giver I got credit for completing the quest. To check things out I received and did the same quest again. Same thing happened, no message, but got credit. I'm sure there are other glitches but this one I remember.)

Got no save before leaving the Dungeon... But its just a days travel from the Guild Hall with boat and I still got like 5 (hopefully more) days left to finish it... Is it likely that it is behind a locked door? Because I found a locked door and my lockpicking skill is really bad (Do you just need skill or also lockpicks? Never found any lockpick...) and I havnt bought/made that spell which allows you to unlock doors...

Anyways, thanks for the advice everyone, stupid that its a specific item that you have to find. :/

Make an Open Lock spell ASAP! Some doors you can bash with your weapon, but this can damage it. And not sure you can open a magically held door without the spell.

There is no way to know ahead where your quest item might be. There is a cheat however:

Locked doors may also be "bashed" in. Just take your heaviest weapon and start swinging. Magically locked doors can only be opened using a spell or by throwing a switch (if available).

There are no lockpicks.

Suggest you make a cheap "open" spell....1 + 1 per 2 lvls....it only uses 5 mana and will open any outside door (including the MG door after hours). Doors (and magically locked doors) inside a dungeon, however, will need a better spell, something on the order of....1 + 4 per lvl....which are quite expensive to use.

Will get a Open Lock spell asap, but the door wasnt magically locked so it would seem that it is bashing time! Didnt know of that before either, a big thanks for the help everyone!

Bashing is very loud, though, and can alert the city guards. So keep an ear out for them.

But he's goin to a dungeon... No guards

Hah, of course! Not paying attention

Good to know when I make my thief, so thanks for the information there too!

I know this doesnt keep up with the earlier theme of the topic but I hope people can answer it anyways (otherwise I′ll just make a new topic):
How do you levitate up/down? And how do you dive up/down? Only managed to swim by pressing my head in under the roof as if it tried to float... :/ And levitating just goes forward when I want to up a ramp and check whats up there.

Oh, yeah, I failed the last mission (was too slow) however got a new try at the same sort of mission so now im trying to learn this complicated dungeon-diving stuff (Oblivion and Morrowind′s caves were like nada compared to this).

Going up and down are controlled by the Page Up and Page Down (default) keys.
However, levitate is ,at times, glitched. You have to be moving (i. e. going forward or turning) at the same time you're trying to go up or down. (e.g. Press the page up and turn left keys at the same time and you'll go up, while turning).

I STRONGLY suggest making a spell that contains BOTH Water Breathing and Water Walking. If you do, I don't think you'll have any problems going up or down. (Water Walking is NOT "walk on water", it is walking through water quickly).

oh man.... always learning something.

this game is truly amazing. I am playing a FINISH HIM sort of mage (High Arcanist). Nothign stands before him .

Aha, I got the Buoyancy spell (water walking) but never found any use for it since there is no water to walk over! Now that I know that its walking through water fast maybe I′ll survive a bit longer down there And Page Up/Down at the same time as turning around or walking forward, got it. Lots of stuff to learn in this game