There is only one legitimate way to cure Vampirism in Oblivion and it requires a lengthy quest to do so.
Follow this link in order to see the details of the quest:
http://www.uesp.net/wiki/Oblivion:Vampire_Cure
You can get a cure for campirism in Oblivion by doing a quest. All the information you need can be found here: http://www.uesp.net/wiki/Oblivion:Cure_Vampirism