this should be fairly straight forward...
open texture you want to use in Photoshop or similar software and apply appropriate effect to 'circularize' it (sorry for vagueness, haven't used photoshop in years and can't remember specific command names).
save as a new texture.
create a new material and assign new circular texture (adjust texture sizing to proposed desk size)
apply material to object and adjust placement of texture with 'aligh texture' tool.
hope this helps.