"How do I get out of this mess?"
USE THE WALK THROUGH. (..and NOT coincidentally it is the 4th "sticky" on this forum.
)
First: "I cannot proceed in the mage class tiers in Skuldoon".
Answer: Look at the section titled "Guildmasters" here:
http://www.gamebanshee.com/dungeonlo...ildofmages.php
Second: "after collecting blood from Valdane, I cannot give it to Vartaag. This gentleman, for instance, keeps insisting that I should get the agreement from lord Davenmor."
Answer: Look at the section titled "After the Naga Temple" here:
http://www.gamebanshee.com/dungeonlo...h/skuldoon.php
*AFTER* having talked with Vartugg *WITH* the vial of blood - check your quest log.. you should *THEN* have the opportunity to place the vial on the alter and actually have it do something.