I'm starting with the basics, b/c I am not sure what is your problem.
Just to make sure, are you level 5 yet? You do not get to select a profession until you are level 5. You must select celt, lurikeen or shar at character creation. By your name, I assume you selected celt so that should not be a problem. After plugging away for the first 5 levels, you go to a vampiir trainer and you should be able to join.
Only other thing to add, although I doubt it applies to you is that you can not /autolevel and still become a catacombs class.