wait...

[Caxton]

I read somewhere that undead get their cha bonus to hp. Am i right or completely wrong?

[Guildorn Tanaleth]

I don't think so. You might be thinking of the fact that (http://www.d20srd.org/srd/typesSubtypes.htm#undeadType) they use their Charisma modifiers for Concentration checks.

[PaladinBoy]

Some undead gain an ability called Undead Toughness which is exactly what you describe: Cha bonus to HP. Not sure where to find it, though.

[Arbitrarity]

It's just a feature of specific undead. You could add it to some, but it's very powerful with some undead (Read: Vampire sorceror, lich sorceror, in fact, most charisma based classes+undead. I.e. necropolitan bard)

See MM3

[BardicDuelist]

Libris Mortis, if I remember right.

[Shhalahr Windrider]

Some undead gain an ability called Undead Toughness...
I believe it is "Unholy Toughness," actually.

I do think that it makes sense for your classic "Mastermind" undead types, such as liches and vampires, to have Unholy Toughness.

[StickMan]

I believe it is "Unholy Toughness," actually.

I do think that it makes sense for your classic "Mastermind" undead types, such as liches and vampires, to have Unholy Toughness.

I think its Unholy Toughness and it only is given to tougher Undead your not going to see Zombies walking around with it. But then I don't think they have a high CHA score so...