I started by creating a new image with a transparent background which was 300 x300. I then set the grid to be 150 x 150 so that I could create a tube with 4 images (each 150 x 150).
I then selected the font called Holidays MT and typed a letter i (lower case) in the first cell. I applied a green cutout effect to this image with settings of Opacity 45, Blur 4 and offsets set to 3. I then applied a white drop shadow with settings of Opacity 100, Blur 1 and offsets set to 1. The shamrocks were created using a lower case o from the same font. The cutout settings were Opacity 75, Blur 4 and offsets set to 3. I used the same drop shadow settings as for the hat and changed the colour to green.

The frame on this images was created using Filter Factory Gallery P filters.