gistfile1.as

//this is part of level.as

var collisionGrid:Grid = new Grid(97,97,16,16);
collisionGrid.usePositions = true;
collisionGrid.setRect(0,0,90,90,true);
mask = collisionGrid;

//and this is in the update method of player.as

if(collide("level",x,y))
{
	trace("collision! ("+x+","+y+")");
	y = oldy;
	x = oldx;
}