Tyranid Rules

[DWOLFF]

Can anyone help me with a few rules that tyranids have?

Preferred Enemy

Pinning

Rending

Beasts

Fleet of Foot/Claw

Swarms

[Skrit]

Uhm, what do you mean? You want the rules of the models? Then I only have one suggestion, buy the Codex!

[mahon]

preferred enemy lets you hit a given type of enemies easier
pinning allows to pin enemies (if they are hit they do nothing for one turn)
rending allows you to add some dice rolls as long if you roll a 6
fleet of someting allows to move instead of shooting
swarms - bases are treated like multi-wound creatures which are more vulnerable to blasts
beasts - i think it makes them faster, doubling the assault range

just straight from my memory, and without going into details not to infringe anyone's copyrights

[Django]

some correction, not meaning to offend;
*pinning only accures when a unit get wounded(fail their and everything) and then fail theirpinning test wich is a normal leadershiptest.
*fleet indeed lets you move instead of shouting but you only get to move a D6.
*rending means every roll to wound on a D6 role of a 6 is auto-wound.
*preferred enemy get you to hit a specific race(or rase?) on 3es in close combat.

glad to help.