Do you have Titanium Backup and ROM Manager installed?
You want to backup all your system data and apps in Titanium Backup. You want to do the Batch Backup/Restore functions in it. That will save all your stuff on your SD Card. Then make a backup with ROM Manager. Then flash a new ROM. Then restore your system data and apps with Titanium Backup.
Now, I am not a flash expert, but I believe that is how it's supposed to be done. This way it separates your data from your OS. Switch the OS and restore all the data. You'll have all your apps and all your settings intact (contacts, apps, login info, movies, music, games, etc).
That's what I've been doing but I haven't been restoring system app data in Titanium, just the app+data.