You can do this quest whether you want to cure yourself of vampirism or not,
but there is no real reward except the cure. You must be a vampire (any stage,
but more than just infected with prophyric hemophilia) to start this quest.
Find Raminus Polus in the Arch-Mage's Lobby of Arcane University during normal
daytime hours. Ask aboue a cure for vampirism and he'll refer you to Count
Hassildor in Skingrad.

Fast Travel to Castle Skingrad and speak to either Mercatus Hosidus (if you
haven't completed "Ulterior Motives" in the Mages Guild quests) or Hal-Liurz
(if you have) about a vampire cure and they'll fetch the count. The count
tells you all he knows; he has himself been searching for a cure for his wife.
(He likes being a vampire, she doesn't, yada, yada.)

He refers you to a witch of Glenmoril who lives in Drakelowe, along the
Carbolo/Reed Rivers in eastern Cyrodiil. Fast Travel to Cheydinhal and head
south; you'll find Melisande inside the one house. She agrees to help you with
a cure, but first, she needs a favor: five empty grand soul gems.

The easiest way to get the soul gems is to buy them. Most Mages Guild halls
have a merchant who has various sizes of soul gems. In addition, the Mystic
Emporium in Imperial City will usually have one or two of that size. Bring
five to Melisand to discover that little scavenger hunt was just the
beginning. The ingredients she wants for the vampire cure will have you
hopping all over the cyrodiil...

Vampire Ashes
For this one, at least, Melisande has a specific target in mind. She wants the
ashes of Hindaril, who resides in Redwater Slough near the east end of Panther
River. (It's actually on the eastern of two tributaries that feed into the
Panther from the north.) At the first T-intersection, turn left (north) to
reach Hindaril directly; however, you'll have to pick a lock to get to him.

If you have little in the way of lock-picking skill, go right (south) at the
T-intersection to find a key. This won't be easy as you'll have to swim
through a flooded tunnel and come up into a room with several undead
surrounding you. The chest with the key is in a corner of the room.

If you happened to clear this dungeon earlier, never fear. Hindaril's ashes
are marked as a quest item, so you couldn't have dropped or sold them anywhere
and you can just hand them over to Melisande.

Blood of an Argonian
Again, this is fairly simple. All you need is an Argonian, any Argonian. You
have a number of choices available to you:

1) Pick an Argonian in any city Bravil and Leyawiin have several each, this is
by far the simplest option if you have the Gray Cowl of Nocturnal (Thieves
Guild)

2) Raid a bandit or marauder hangout, searching for Argonians

3) If you've finished the Daedric Shrine quests (or most of them), find an
Argonian worshipper at the shrines of Azura, Boethia, Hircine, Peryite and
Sheogorath

4) You’ll find an Argonian (Skaleel) on the first level of Vahtecen, but she’s
off-limits if you’re a member of the Mages Guild.

You don't need to kill the Argonian, just hit him once with the special dagger
given you by Melisande. Of course, that will make the Argonia and nearby
friends hostile, so choose your mark wisely.

Nightshade and garlic
You can pick these up at alchemist shops; there's one in every Mages Guild
hall. You can also try The Main Ingredient and the Gilded Carafe in Imperial
City's Market district. That should be all you need to get the five nightshade
plants and six garlic cloves.

Bloodgrass
This plant typically grows only in Oblivion. If there are Oblivion gates still
open, you can pop through and pick up two samples pretty quickly. If not, you
can try the Daedric quests of Boethia and Peryite, both of which send you to a
special Oblivion plane, where you might be able to find some bloodgrass.

If the gates are all closed and you've previously finished the Boethia and
Peryite quests, you may still find some bloodgrass growing around the wreckage
of closed gates. Or, you may get real lucky and some alchemist has some in
stock. If you've purchased the Wizard's Tower official plugin, then head
straight to Frostcrag Spire--you can get two samples of bloodgrass in the
conservatory next to your quarters.

The cure
Once you have all the ingredients, hand them over to Melisande. You then have
to Wait 24 hours to get the cure. Return to Castle Skingrad and talk to
Hosidus or Hal-Liurz again and you'll be escorted to a secret room where the
Countess lies in a coma.

Lo and behold, Melisande is there before you. She revives Rona Hassildor long
enough for her to drink the cure and then she dies. If you try to talk to the
count, he'll brush you off with a request you wait a day to allow him to set
his wife's affairs in order.

Wait 24 hours and ask the steward for the count. He'll come down and
officially conclude the quest with a small reward. And, oh yeah, you still
have one dose of the cure to use on yourself. If you later get vampirism
again, you have to repeat the ingredient gathering for Melisande in order to
get another dose.