If you have an ISO image it means that the cd image was extracted with a program like Easy CD Creator, the WORST program for duplicating a PSX cd!
Now you have 2 choices:
1) Use NERO and import the cd image (mode 1)
2) [BEST] Use CDmage and convert the image as CDRWin image (bin + cue) and burn it with CDRWin
Only a few old games can be duplicated with EasyCd (i.e. Dead or Alive), so if the game is recent probably it won't work...
If U are searching for CDmage (incredible and useful software in my opinion) go to
http://cdmage.cjb.net
Good Luck