Remember this key can't be used right now, you will have to wait until Monday 8 PM CET. At this time, EA Phenomic will be opening a new game server for Tiberium Alliances and everyone is invited to play on both. No second key is needed, as one closed beta account entitles you to play on both. So if you're already in the closed beta, you have something look forward to. This is all part of EA Phenomic's planned "Stress Test". They want as many players in the game as possible to see how their servers hold up.
I'm not 100% certain, but I think this key is either unique to CNCNZ.com or the English speaking C&C community. So your chances of getting in should be good, but it will go fast, so you're going to have to be quick. It's first in, first served.