What follows (below the quotes from Steve Marsh) are my interpretations for optional rules on dealing with vampires in BX/LL D&D (though I suppose it could also be used for all the other early editions as well, without much issue).
From an ongoing Dragonsfoot Forum Discussion
with Steve Marsh, circa 2005/2006:
"I wanted vampires to require different steps to kill them, basically each step reducing the number of hit dice they had: so stake a vampire, reduce it by 12 hit dice. If it is 12 or less, staking it reduces it to dust. More than 12, then you need to add a step, such as cutting off its head, or stuffing the head with garlic, or burning the whole thing and burying the ashes at a cross roads). -Sat Jun 24, 2006 1:48 am
"I also wanted to do a step reduction for Vampires. Stake them - 10hd. Cut off the head -6 hd. Stuff head with garlic -4 hd. Bury at cross roads, double hit dice reduction. That way, to kill a vampire really dead (so it would stay dead) would require various parts of the classic treatment depending on how powerful it was." -Mon Apr 11, 2005 5:43 pm
Optional Rules for Killing Vampires (Long Version)
For all of the following methods, a vampire that has lost HD (i.e., "levels") may only regenerate 1HD per day, and my only regenerate a total number of hit points that does not exceed his relative total per his current HD. Reducing a vampire to 0 (or fewer) HD and 0 (or fewer) hp permanently turns the vampire to dust.
Sunlight: If exposed to direct sunlight while conscious and if his movement is not restricted (e.g., the vampire may not be tied down), the vampire must save vs. death ray for each round of exposure or lose 1HD and a relative number of hp (e.g., a vampire with 10HD and 80hp will lose 1HD and 8hp). If exposed to direct sunlight while unconscious, or while movement is restricted, the vampire automatically takes loses 1HD and a relative number of hp (no saving throw).
Wooden Stake: A wooden stake in a vampire's heart immediately reduces the vampire by 10HD and a relative number of hit points. If the stake is removed before the vampire has been reduced to 0hp, the vampire will regenerate HD and hp as prescribed above.
Silvered Weapon: A silvered blade in a vampire's heart reduces a vampire by 1HD and a relative number of hit points for each round it remains lodged there. If the silvered blade is removed before the vampire has been reduced to 0hp, the vampire will regenerate HD and hp as prescribed above. A silvered blade may not be lodged into a vampires heart if the vampire is already staked. Likewise, a wooden stake may not be lodged into a vampires heart if a silvered blade has already been lodged there.
Fire: Damage to a vampire by fire deals hp damage only, and does not reduce the vampire's HD.
Removing a Vampire's Head: Cutting off the head of a vampire reduces it by 6HD and relative number of hp. If the vampire's head is returned to it's proper place atop the body before the vampire is reduced to 0hp, it will re-attach itself in 24 hours. Stuffing the head with garlic lowers the vampire by an additional 1HD, and prevents the head from being able to re-attach itself (unless the garlic is removed first).
Burying the Vampire at a Crossroads: If the vampire is buried face down at a crossroads, any HD loss and hp damage is automatically doubled, once the dirt over the coffin has been packed down and the site is blessed by a cleric.
Optional Rules for Killing Vampires (Short Version)
Sunlight: Exposure to direct sunlight reduces a vampire by 1HD for each round of exposure (no saving throw).
Wooden Stake: A wooden stake in a vampire's heart immediately reduces the vampire by 10HD.
Silvered Weapon: A silvered blade in a vampire's heart reduces the vampire by 1HD for each round it remains lodged there.
Fire: Vampires take normal damage from fire.
Removing a Vampire's Head: Cutting off the head of a vampire reduces it by 6HD. Stuffing the head with garlic lowers the vampire by an additional 1HD.
Burying the Vampire at a Crossroads: Burying a vampire at a crossroads immediately doubles any HD and hp loss.