This is a beginner's tuto .. You probably have a better way , but i do this and it's really easy
Like these :
First of all , take a wooden texture like this one :
http://mayang.com/textures/Wood/imag...re_9271241.JPG
Resize it , and then you can start working . For instance , you can add a "plate" on it . Copy a piece of wood , then make a new layer and paste it there . Add some filters/noise/darken it a bit so you see it's not supposed to be a flat piece of wood . You can also bump it if you want :
Now , make a new layer . Here , draw 4 circles (they don't have to be perfectly round) with a fuzzy brush :
Now , start adding highlights with a small soft brush , and counter it by darkening the other side of the nails . You can also add some highlghts with a splatter brush (galaxy big in GIMP) , and bump it a little .Then darken the area under your nails (on the second layer) , and you are pretty much done :
Now just merge all layers and you're done