I partially agree about transferring clans into AdC, and giving each clan access to specific Talent Trees for the Disciplines. Basically, looking at this way, a clan is a 10 level AdC. It has access to three Talent Trees (Disciplines), and gains a Talent at every level. That might sound like a lot, but think of it this way -- a 10th level Gangrel would have only 10 Talents that he would have to spread throughout 3 Disciplines, so the maximum he could have would be two Disciplines at 5 (usually the max for a standard WoD vampire), which, with an eye towards equivalences from conversion, a 10th level Any Clan PC would have around 11-14 levels -- the Clans are AdC, with their only requirement being to be Embraced, hence all players will have at least one level in a Basic class to begin.
A 14th level character in D&D is roughly equivalent (from experience and gameplay, and probably power levels as well) with an Ancillae or Elder vampire in WoD. But remember, as D&D is a class-based system with Skill Points, and WoD is entirely point-driven, there will be massive inconsistencies in crossing-over.
In WoD, a character gains XP that they horde until they are willing to spend it on improving an Attribute, Skill, Discipline, Background, or Willpower. In D&D, many of these things advance automatically has a result of leveling, and do so in a manner wholly different from WoD. It will be almost impossible to capture the feel exactly in the cross-over, because leveling in D&D represents becoming a better member of your class -- if you translate Clans into AdC, then leveling in the AdC represents becoming a "better vampire," often at the loss of access to your human side. On the other hand, if you level in strictly Basic classes or non-clan AdC, you'll never become more than a neophyte vampire, and the powers of the Elders or those who decided to shuck other avenues of advance for the Clan AdC will run roughshod over you.
Another idea for translation -- gut the existing Vampire template, and use it to create several Vampire Clan templates. Create Talent Trees for each Discipline as above, but now, whenever a vampire character receives a class-granted Talent choice, they can select to advance a Discipline Talent instead (with DM approval, because Disciplines should only advance if the character is using them regularly). However, since every Clan is different, they only still have access to a limited number of Disciplines. Make a Special Feat that must be taken using a General Feat (or with special story circumstances as part of its prerequisites) that allows a Vampire ACCESS to another Discipline Talent tree that they can spend feats/Talents on. This option forces PCs to select between becoming more powerful as a vampire, or advancing their class abilities. Since only Basic Classes presently allow for Talent Tree choices, a vampire wishing to advance their Disciplines would have to multiclass in Basic classes (which would affect their overall power level because they would not have the special skills of an AdC) and they would also be losing out on the Talents offered by those classes.
Still, even in that option, there are inconsistencies and potential abuses. Some classes have very nice Talent Trees, while others benefit from better saves and skill point allotments. There has to be some balancing involved to make it alright for players to be Vampires in a group that doesn't necessarily have all vampires.
