Okay, are they required to use the spell or attack power? Like can a warlock have a greatsword in two hands and still use spells?

They are not required. The implements add a bonus to your attack rolls and damage if they are enchanted and also offer some other bonuses even if they are mundane, but you can cast the spells as written without them.

As for whether spells can be cast with your hands full, I couldn't find any other ruling than a small mention on page 54 that the DM might rule you can't use your powers on a situational basis and the example it gives is if your hands are tied. If it written in plain english somewhere else, I couldn't find it.

From my understanding those that use implements are not required to use them when casting their spells/prayers. Although they would not get the enhancement bonus to attack and damage from a magical greatsword as they would some sort of magical implement(say a wand). At least that is my understanding, because if you read the implement section of both the wizard and warlock it says that they can still use their powers without implements.

EDIT:Man, I was a minute late, should have refreshed before posting.

Athough he can, it only seems feasable at lower levels, when he doesn't need the higher attack bonus to overcome enemy defenses.