I want to give Darky's ROM a try on my Samsung Galaxy S; I'm currently running CM7 RC1. How would I go about doing this? Can I flash using recovery, or do I need odin? Do I need to revert to stock first?
Most Darky's packages I've seen are your normal update.zip variety that are flashed through recovery, so you should be good to go. If it's an Odin package it should say so — always vet your sources (here's a good one).
I see no reason to believe flashing from CM would be a problem either unless it messed with your partitions. If you have problems you can always Odin to stock and then root, install ClockworkMOD, and flash Darky's again. The whole process only takes a couple minutes. (So if you're concerned, go right ahead and Odin to stock, it costs you nothing; just save your backups to a PC first.)