cant you just wait until your a higher level?
i did this when i was about lvl. 13, and it was easy. i didnt use any magic, cos im a warrior. i wacked em with my sword to kill em, good old fashioned way!!
yeh, idid get vampires disease, but i cured that with a visit to the chapel. also, when i paid em a visit, an orc ahd a nice set of ebony armour, which helped me alot through some tough bits in the game. plus you get some nice weopans to. its a win-win situation! ( exept for maybe getting killed)
with the zombie-making man, just use some good magical weopans (did i spell it right?) or, just ignore the zombies, and go for the vampire instead. then when he's dead thezombies go. simple as!