I once used this little snippet to animate the UVs of my plane, for a similar purpose:

This was for an 8x8 grid. The 'padding' value determines how much inside the border of each grid cell is actually sampled - to avoid 'bleeding' between animation frames.

It returns a list of two Vector2s. The first is the lower-left corner of the animation frame, the second contains the width and height of the animation frame in UV units.

Vector2[] GetSpriteUVs(int frameNum)
{
    int gridSize = 8;
    float padding = 0.1f;


    int x = frameNum % gridSize;
    int y = (gridSize-1) - (frameNum / gridSize);

    float u = (float)x / (float)gridSize;
    float v = (float)y / (float)gridSize;

    u += (1.0f / (float)gridSize) * padding;
    v += (1.0f / (float)gridSize) * padding;

    float w = (1.0f / (float)gridSize) * (1 - padding * 2);
    float h = (1.0f / (float)gridSize) * (1 - padding * 2);

    Vector2[] uvs = new Vector2[] { new Vector2(u,v), new Vector2(w,h) };

    return uvs;

}

Another option would be to take a look at the SpriteManager script on the Wiki, which has this functionality built-in.