Okay, not arguing the ethics of using evil characters like vampires and werewolves and such in a campaign, I want to talk about ECL and experience after character creation.
A vampire is a +8 level adjustment, as it should be. This means in a ninth level party a vampire can start with one character level. Fine.
If however, a character is infected with vampirism later, this modulates their level then. Say this happened to a character with 13 character levels, as it did. This would bump the character up to an epic level character, or 21st level. Fine. Now, would their experience point total jump up to the minimum experience neccessary for a 21st level character, or do they have to make up the debt?