Changing HDD in my PS3 - Question about backing up data.

I'm tired of worrying about how much space is left in my meagre 40gb so I've bought a 320GB. I have a USB pen thats only 16gb but could easily back up my saves if I removed a few of the PSN games and mandatory install data.

I bought a caddy with it as well. Since I ordered this, could I put my old 40gb into it, put the 320gb into my PS3 and just switch the data over to the PS3 from the now external 40gb?

No, you need to do a total system backup, especially if you want your copy protected saves. A lot of saves you could just move to a flash drive and do it that way, but either way you can't just use the current harddrive as the external immediately.

Delete all your game install data and a total backup should fit onto a 16GB flash drive. The game install data seems to screw with the total backup for some people anyways. Then pop the new one in, let it format it and such, then restore from the flash drive. bam you're done.

(Don't do anything to the harddrive that was in the PS3 until you're certain everything backed up correctly.)