Ok last month i got the 120 gig slim. so may be some day in the future i will up grade the harddrive.
 then i read that will will need FW3.1 on a thumb disc to make the new hard drive work.
 so i called  sony 2 times and i asked them if i have the slim updated to the newest fw
 will i need to have the fw on a thumb stick to make the new drive work.
both people i talked said no. and i aslo asked if i can burn the fw up a disc and they said yes.
 so did any body try this yet and should i trust sony ..?? if i wanna update some day

I think only the original 60GB and 20GB can you replace the HDD without needing the FW on a thumb drive. I would have it ready just in case, I am pretty sure you will need it.

thanks vette man if i do the upgrade i will have it ready lol.
i know when i had my phat all i did was just put the new drive in and it was done

I'm pretty sure you need a recent firmware not necessarily 3.1

Firmware is stored on an internal flash memory. Are you sure you called Sony? They wouldn't be this stupid. If it was on HDD, it would be to easy to modify.

Are there directions included in the manual that came with the slim for this procedure?