I have a Dell D620 with a locked bios password, it wouldnt let me change the boot order or adjust any of the bios settings. So I made the DST floppy, ran via a usb floppy drive, had sucess. It erased the password and servicetag. My question is do I need to put the srevice tag and express service code back in, or should I leave it blank?

I would put them back in. That is in case you have service done on it.

Does the DST CD help with the unlocking of bios password?

Just leave it blank