I have to admit that the rules (or at least the procedural flow) isn't being made explicit.  

Two new tanks are rolling out to the field of battle in Warhammer Online during a two-week long Heavy Metal event that began yesterday.  The Empire Knights of the Blazing Sun are the veritable poster children for WAR, while the Dark Elf Black Guards have enough spikes on their armor to serve shishkabab at a Chaos warhost high school reunion.  But to be fair, both look downright gaudy in their peacock-plumage of overlapping metal plates, curvy spikes, and thickened feathers.

But how you get your hands on one of these bad boys, exactly -- that's what's not being made explicit.  The press release simply instructs people to "successfully complete the quests associated with the Heavy Metal event" to be given week-early access to the two new classes.  Well, after logging in this evening, I found no further instructions on how to unlock this new class.  I'll admit, I'm still having too much fun setting the roof on fire with my Bright Wizard, Pitchfork, but that doesn't mean I don't want a peek at these two guys that are crashing the party in such a high-profile manner.

Trashing enemy players at the Reikland Factory -- a new realm vs. realm scenario opened up especially for this Heavy Metal event -- is the only breadcrumb I've stumbled across.  And after playing through Reikland Factory a few times with Pitchfork (scoring 3rd, 4th, and 7th in number of kills -- not bad for being 5th level when 10th level players are on the field, and doubly not bad when there's 36 -- 18 vs. 18 -- people duking it out), I'm still feeling no closer to completing the "quests associated with the Heavy Metal event." 

I'll keep eyes and ears (not to mention a few scalps) peeled. 

EDIT:  A-ha.  I guess when it comes to the Warhammer Online site, I'm not so much with the reading.  Here's what I've found to answer my own question:

"When the Heavy Metal live event begins on November 18th, players who log into WAR will see a new tab in the Tome of Knowledge. Clicking on this tab will open the Live Events page, where each day we'll place a new daily task. Completing these daily tasks earns influence, just like you'd earn in a public quest. There are rewards for Basic, Advanced and Elite influence, culminating in the ultimate prize: the chance to play WAR's new classes a full week before they're released to the public! This last reward won't be easy to earn, and players who want to get to the Elite level will need to log in each day and complete on the daily event."

Very well then.  Question answered.  Crisis averted.