Hello,
Don't know quite what you were trying to do but I hope this helps some.

// frames 0-11 = walk RIGHT
// frames 12-23 = walk LEFT

if (RIGHT key pressed)
{
if (captin.activeFrame > 11)
captin.activeFrame=0;
else
captin.activeFrame++;
if (captin.x < 220)
captin.x++;
}
else if (LEFT key pressed)
{
if (captin.activeFrame<12 || captin.activeFrame>23)
captin.activeFrame=12;
else
captin.activeFrame++;
if (captin.x>0)
captin.x--;
}

// Do sprite stuff here....

Again, hope that helps a bit.

Martin.