I noticed that according to current SR4 resources, Vampires no longer have the Enhanced Attribute power. As far as I can tell the enhanced attribute power no longer exists in SR4! Am I missing something? Or can vampires no longer arm wrestle trolls?

You are correct. There is no longer an Enhanced Attribute critter power at all. Since vampires can be awakened, it's obviously possible to simply use the Increase Attribute spell to simulate this.

SR4 page 294...

"Many vampires display magical ability, and the transformation sometimes unlocks hidden magical potential. Such vampires are capable of learning and using magic just like a human. Vampire sorcerers are most likely the source of some legendary vampiric powers, such as the ability to change into animals or to mesmerize victims."

Its listed under the Essence Drain power and it is completely nerfed. If the vampire has fed in the last hour it can spend half the essence points it gained from that feeding to enhance 1 attribute by 1 point per essence point spent for 12 hours.
However, this can be used to enhance Magic and mental attributes.

Hmm. So, skip the vampiric magician. How about a vampiric adept? You feed. You spend Essence to increase your Magic for the next 12 hours. Does this give you additional power points with which to buy further Adept abilities (at least, until your Magic drops again)?

That vampire could get really ugly really fast.

I dont think that raising your magic like that would give the adept vamp more powers. But if you want the goon vamp in your game to drink blood and go into some crazy blood frenzy with extra powers.. more power to you my friend.

I'd say it would increase the Magic rating for purpose of things like max casting force and the like, but having it grant new and interesting powers is a little much.

...

Then again, if the character had those powers LAID OUT AHEAD OF TIME, I'd probably allow it.

"Yeah, when he drinks Essence, he gets really amazingly fast. Can frickin' grab arrows out of the air, man, I've seen him do it..."

Basically, write down the powers that you get when you've got 1 point of "Drained magic", 2 points, 3, etc.

You do understand that there is no canon way for PCs to gain the essence drain power and there never was in any edition, right?

If a vampire can gain extra adept powers it would be pure GM fiat with is okay because all vampires are NPCs.

Are PCs immune to HMHVV? Or does the player just lose control of the PC when they get it?

It's not like I'm going to have vamp characters in my game... I'm just barfing out a rules idea in case it were ever to occur (or someone else wanted to do it).

Actually the vamires gaining new powers wouldn't be any different from the SOTA 64 version of a metamagic technique (can't remember the name of it though.) Basically it allowed you to increase the level of a current power by a bunch and/or have a new power(s) at rating 1. This could get particularly nasty with attribute boost.
Most people I know play that a PC that contracts hmhvv becomes an npc.

Characters transformed by HMHVV (except ghouls in some editions) become NPCs.
However, it is almost impossible to be transformed into a vampire. Doing so requires that a vampire kill you with essence drain. Essence drain requires that the drainee be incapacitated or willing, requires a strong emotional bond, and takes several minutes. It isn't something that happens except as a plot device.

The rules for Krieger strain in editions that have them allow a very generous resistance test and it is possible to cure it with treatment within the first 30 days after exposure even if you fail the test.

HMHVV-II is the most likely canidate for an infection. I'm not sure if there are actually rules for HMHVV-II infection anywhere. Critters certainly doens't give any specifics. At any rate, there is still a resistance test.

Only HMHVV-I confers the essence drain power.

They need to just come out and make rules for players being vampires eventually, because you know every damn gaming group has thought about going that route at some point. I'm not a big fan of it, but it's what people want.

I tease my Ork player that she will be get infected quite a lot when the subject comes up. She dosen't like the idea of playing chewbacca though...

On the list of "Things people think are super cool" Vampires are right up there with Katanas and Ninjas....

Blame it on Anne Rice and her angtsy sexually impotent ubber-munchkins.
I much prefer the Bram Stoker's good ole' amoral asshole vampires with hot bisexual vampire slaves.

Dikoted katana/AVS gunblade ally spirit...

...which, as hyzmarca pointed out, is bisexual, so whoever you are you can sleep with it.