How do you get turned into a vampire? Just by having one fight you?
Drinking a vampire's blood. This is usually easy enough as stabbing one and licking the blood off your sword.
Being a vampire is wonderful. You don't need to eat, drink (normal fluids, anyway), or sleep, and zombies totally ignore you. If you wanted, you could stroll through an entire necromancer's tower unmolested and stab the necromancer in the face. When you become a vampire, some of your physical stats are doubled. On top of that, you don't feel pain, don't suffer exertion, don't need to breathe... You're effectively a living god of combat.
There's a couple issues, though. Vampires need to drink blood from living, unconscious opponents, which can be hard to come by without turning an entire civilization against you when they wake up. After your physical stats double, they also
lock so you can't improve them further. Even with these problems, being a vampire is awesome.