If you have issues getting a ROM to work through ROM manager you may want to make sure you have the right clockwork installed in the ROM manager and there aren't any updates available. Another thing to make sure is take your time and make sure you check "clear data/cache" and "download google apps" for Cyanogen.
I'm guilty about buying the app to support the Dev but I mainly just manually install all the roms straight from clockwork recovery because....well I have a control complex
I like to know the phone is taking the right steps even though I know ROM manager is more than capable. It just depends on what I'm doing.
So bottom line take your time and READ READ READ the threads on your ROM. I know they are long threads but you need to get caught up on whats changes, what issues there are, and what work arounds or fixes there are and what they do. Read the ENTIRE thread at least once then you can skip to the last page or two. For instance pmf has rolled his 1.2 version back to 1.1 with a policyupdate.zip because of an issue he had. etc etc.
Good luck guys and have fun!