Oblivion:Darkness Eternal

[edit] Quick Walkthrough

After the Dark Brotherhood quest The Assassinated Man, speak to Vicente Valtieri and select the topic "Dark Gift".
After Vicente agrees to visit you in your sleep, find a bed to sleep in.
Upon waking up you will get a message indicating that you were visited and that you have contracted Porphyric Hemophilia.
After 3 days sleep again and you will be a vampire.

This quest must be started before The Purification quest has been finished, and should you wish to take Valtieri up on his offer, that must also be done before the end of the same quest.
The quest can only be ended and removed from your active Journal list with the death of Valtieri.
Even if you have 100% Resist Disease you will still get Porphyric Hemophilia.
If after getting the disease, if it is cured (through the use of a Cure Disease potion/spell or an altar) before three days have passed, the quest will stay in your journal, and Vicente will not give you another chance. Therefore, it may be a good idea to just re-activate the bed and go back to sleep for the 3 days.
If you have previously become a vampire, and been cured, you can not become one again, so this quest will not work.
After you become a vampire, you can ask Vicente about a cure for vampirism.

Darkness Eternal (DarkVamp)
Stage	Finishes Quest	Journal Entry
10		As a reward for my loyal service to the Dark Brotherhood, Vicente Valtieri is willing to turn me into a vampire. If this is my wish, I should speak to Valtieri about the Dark Gift.
20		I have accepted Vicente Valtieri's offer to turn me into a vampire. The next time I sleep in the Sanctuary, Valtieri will visit me and pass along his Dark Gift.
100		Upon awakening, I discovered two bleeding pinpricks on my neck. It would appear Vicente Valtieri did indeed visit me last night, and pass along his Dark Gift! If what Valtieri told me is true, my vampirism will begin to manifest itself in three days, after I sleep once more.
110		Vicente Valtieri believes there is a cure for vampirism. If I wish to investigate further, I should speak with Raminus Polus, a mage who has done some research into the subject. I can find him in the Imperial City, at the Arcane University.
115		Vicente Valtieri is dead. If I wish to become a vampire, I must seek another means of acquiring the Dark Gift...
116		Vicente Valtieri is dead. If I need further information on vampirism, I'll have to find it elsewhere...

Not all Journal Entries may appear in your journal; which entries appear and which entries do not depends on the manner in which the quest is done.
Stages are not always in order of progress. This is usually the case with quests that have multiple possible outcomes or quests where certain tasks may be done in random order.
If an entry is marked as "Finishes Quest" it means the quest disappears from the Active Quest list, but you may still receive new entries for that quest.
On the PC, it is possible to use the console to advance through the quest by entering setstage DarkVamp stage. Where stage is the number of the stage you wish to complete. It is not possible to un-complete (i.e. go back) quest stages. See SetStage for more information.