I just ported my demos Led Blur and Creep Tea from GCW0.
They wouldn't run just by copying the older OPKs, because mikmod lib doesn't seem to be present anymore, so I replaced the player with SDL_mixer.
The OPK that would still run intact, is my shader tests on GCW0.
All provided with source code too.
p.s. Sorry, but I don't know how to direct URL on the ftp links. Just copy paste on browser to download.