For future reference, please direct all questions regarding rules to the Rules Forum please.
1) All Equipment has a uniqueness tag on the far right side of the type line. This dictates how many of a given type of card you may have in play at once. If you had a 'Melee (1)' weapon in play, and proceeded to play a second with the same tag, you would immediately have to destroy one to end the uniqueness violation. Of course, the Dual Wield power allows you to have up to 2 one handed melee weapons in play. If a card would ever contradict the written rules, the card is always correct, so you could have both in play.
2) There are primarily 2 types of constructed tournaments, normal constructed and Block constructed.
In normal constructed, you may use any card released to date. There are no Banned and Restricted cards, and every set/special release is legal.
Block Constructed only allows use of cards from sets and special releases during the most recent block. Block Constructed generally only sees play after the third set in a Block is released.
Full details of formats and legal sets can be found in the Policy Documents, located here:
http://entertainment.upperdeck.com/COMMUNITY/files/28/english/entry1840145.aspx
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