I'm pretty sure Dell oem files require strings in areas that cant be edited in with dmi tools alone. Its best to use sets that only require one string in the manufacture DMI area like HP. These can be edited in using dmi tools in most cases.
Its a small DOS based app that writes the SLP string to the bios instantly without the need to flash. Look a few pages back I uploaded a bootable cd iso with the tools on there. Its called Hewlett Tattoo SLP Boot Disk or something to that effect. You will need to get a HP OEMBIOS file set to place inside the I386 folder of your XP disk however and they are two differnt sets depending on what HP string you choose. One requires the slp string "Hewlett-Packard" and the other set is for string "HP Pavilion". Look at the XP Key collection sticky at the top for a slp key to use.
Ok to start with you need to say what type of bios it is i think peeps here are thinking you are trying to mod a dell bios through using DMI,let us know what your bios is i,e AMI, AWARD, e,c,t. you can edit DMI but we need more info..