ah yes I forget to mention there is no file browser app on CM9 for some strange reason, no idea why, I had the same problem, don't worry everything will still be on sdcard, just open browser at this address to install file browsing app
http://openintents.googlecode.com/files/FileManager-2.0.2.apk before you download goto options and tick to download from unknown source.
EDIT: yes CM10 has file browser so you will find all your files.
EDIT: To make a nandroid backup first power off phone then hold Volume UP+HOME+POWER that will take you to recovery mode, scroll down (using volume buttons) to "backup and restore" then select "backup" (using power button) wait for the backup process to complete then reboot your phone, and you’re done. You now have a complete backup of EVERYTHING on your phone memory.