@Nouw: Registering for the prerelease is easy enough. You just give one of the staff your name and which one of the five guilds you'd like to represent. Depending on your choice of guild, you'll receive a guild pack, at the event, that contains almost everything you need.
A Guild Pack contains six booster packs, five randomised as per usual and one tailored to your guild of choice. You use the cards you get in the packs to build a forty-card deck: this type of tournament is called
Sealed Deck. Ideally you want 23 nonland cards and seventeen lands in your deck (you can get basic lands for free from the store's stocks of each, but only during prereleases and drafts and such). You're usually allowed half an hour for deck construction, after which you play a few matches against other participants.
Most people will probably be willing to help out an inexperienced player, myself included. If you want I might be able to help with deck construction as well, though I won't know for sure until I see my own card pool. XD
The guild pack also includes an achievement card, which you can complete if you like. I dunno if there's a reward for doing so: you might get a promo card.
With all of that out of the way, which guild do you think you'll go for? The guilds featured in Gatecrash are Dimir (blue/black), Orzhov (white/black), Boros (red/white), Simic (green/blue) and Gruul (red/green). Each one has a defined style of play and a unique in-game mechanic. Do you have a preference for any particular colour?
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A short message to the less Magically inclined: Sorry if I'm hijacking the thread a little.