Making iconsets is easy, understanding how directory opus handles icon sets is a bit of a learning experience.
Icons [Directory Opus Manual]
This user script is for beginners, (just use any images, converted to PNG)
Iconset Maker (Updated) - Icons - Directory Opus Resource Centre
This user script is more for professional and dual mode (non-scaled) sets
Iconset Maker Pixel Perfect (Updated) - Icons - Directory Opus Resource Centre