well, obviously I had this major problem earlier, by getting the vampirism and the corprus at the same time, which wasn't easy...anyway, the next time I played Morrowind, I figured it all out...
I can't remember the name of the cave or the place where I were, but it was on the second main quest, where you have to kill Dagoth Ur....
Anyway, I found these beasts in Red Mountain as well, while doing in a simple quest, and you can also find some all around ghostgate, especially higher up.... in any case - these 'things' look like a troll, but they have huuuge masks and tentacles sticking out of their faces. They don't notice you easily, unless you stand in front of them. What happens if you meet one?
first it casts magic at you.... anti-resistant to fire or something - down to only 50%.... then if you haven't killed it by then, it will turn you into a vampire....with magic! go figure... anyway, I could never understand WHY or HOW I had turned into a vampire, because there were no human/vampires in that cave...and then I actually stumbled upon one in Red Mountain and voila!
Second try went much better
ok...let's see then
The little island north of Gnaar Mok. That's the cave you encounter in the second test on the main quest...so - if you want vampirism..try yourself in that cave