I can absolutely guarantee that flashing a new firmware will not touch the photos and videos, so you've no need to worry about them disappearing.
The bad news though is that there isn't a firmware available for download for your Meteor locked handset. Now for the good news, You can flash it with the latest official Gingerbread which you can download from the link at the bottom of this post.
To flash, first extract the folder you have downloaded to reveal two more folders (Odin and the JVT firmware package). Now extract those two folders to your desktop.
First of all make sure the phone has at least 60% charge.
Now switch off your mobile and leave it until it vibrates (can take up to 10 seconds) and then put it into download mode by holding Volume DOWN + Home button + Power button. The screen will have a yellow warning triangle with the Android robot digging.
Now launch Odin and connect your phone to the PC. The box under ID.con should turn yellow with some text in it to indicate the phone has been recognised.
Now click PDA and navigate to the firmware folder you extracted earlier and select the CODE file.
Click PHONE and select the MODEM file.
Click CSC and select the CSC file.
Now click start and go and have a cup of tea while it does it's thing.
When it's done the phone will auto reboot but will take a lot longer than usual to fully reboot. Don't worry as this is normal on first boot after flashing a new firmware.
If for whatever reason the process fails, just repeat the above steps to recover.
The very best of luck to you.