To get to Nandroid, you need to flash a custom recovery. To flash a custom recovery you need to unlock the bootloader of the device.
I prefer doing it myself. While the all-in-one toolkits can do it easily, I prefer knowing what I'm actually doing instead of letting a program just flash what it wants willy nilly.
In a nutshell, you need to get adb and fastboot programs on to your PC here: http://dottech.org/downloads/adb_fas...ther_tools.zip
Just extract them to a folder of your choice, C:\Android, for example. You then need to set the PATH variable to this folder for command prompt.
When this is done, you should be able to use the fastboot and adb command in command prompt. Test this by just typing "fastboot" without quotes, and it should show you all the options.
Power off the device, then hold the power button to power back on, but hold the volume down key as well. You should boot in to the bootloader. Go to fastboot with the device connected to the PC. In command prompt, type "fastboot oem unlock" without quotes. I'm not sure if this wipes all data, or not, on the Nexus 7, so may have to do some research.
When that is done, you can then flash a custom recovery. Go here, and download the Touch Recovery for the Nexus 7 (184.108.40.206). Put the .img file on your C:\ and open command prompt again. If your device has booted back up, type "adb reboot bootloader", so you get back in to the bootloader. Type "fastboot flash recovery C:\recovery.img" (recovery.img being then name of your recovery). It should flash the recovery. Once it's flashed, in fastboot on the device, go to the hboot option, then go to the recovery option, and you should be in recovery. You can then use the backup/restore options. Backup will do a full backup of your device and store it on the sdcard in clockworkmod/backups.
If you can't use the adb or fastboot commands, go to the developer settings on the device and enable usb development.
This is only for some guidance, I'd research everything yourself until you're comfortable with what you are doing. You can't brick the device doing any of this. You can only brick your device completely if you start flashing bootloaders etc, but be careful nonetheless.