As far as vampires in Tunnels & Trolls go, very little is known about them, but what we do know through various rules makes them pretty interesting characters. Firstly, they are part of the rare kindred roster, boasting average or higher attribute modifiers: STx2.5, CNx1, DXx1, INTx1.5, LKx1.5, CHRx2, WZx1.5. It's important to note that vampires can only be Specialists or Wizards, so evil vampires are likely to come loaded with a bunch of relevant spells, such as: Knock Knock, Mirage, Spirit Mastery, and possibly Fly Me. The rules also explain that vampires are shapeshifters. We can presume that this is a reference to Dracula, who could turn into a bat and a dog, but there are no real rules for transforming into an animal. Here's one I wrote that you can use:
Shapeshift: Make a INT SR of your level + 1. If you succeed, you transform into a bat or a dog. Your items and armour fall onto the ground. You may change back to vampire form by making another SR. You may only shapeshift once per day.
There's also no mention of sunlight harming the vampire. Depending on what mythology you subscribe to, this may not be applicable and indeed if you're playing as a vampire delver, it may be undesirable. In this case, you could rule that vampires staying out in the day for over 5 hours will take 5 CON damage and then 5 for every 15 minutes after. Otherwise, you could rule that as long as the vampire is covered from head to toe then the daylight has no effect, but as soon as the daylight hits them they take 10 CON damage every 15 minutes.
You should also decide whether you will play as the solitary vampire, the charismatic loner who only joins others if there's something in it for him, or whether you want to be a social creature who regularly attends extravagant parties at wealthy noble houses. Or maybe you want to be a more feral vampire, who is unpredictable, even for the delving party. All of these ideas offer some good roleplaying opportunities but it's worth discussing them with your fellow players too.
So whether you want to run a vampire-centric campaign as a GM, or become a vampire delver, I hope this post has given you some ideas. Now go suck some blood.