Not really Adinu, many Inspiron 600m's shipped with the EXACT same board that D600's shipped with. One is neither better, nor worse than the other. The only real difference is the presence of LPT and COM ports (if the laptop didn't have these before) and Gigabit Ethernet.
If you REALLY REALLY REALLY want to change your BIOS, you can download the latest BIOS update for your system, boot to DOS mode via CD or floppy and run the i600mA##.exe with the /jabil or /forceit switch (i can't remember which one works) That'll have you back to running an Inspiron BIOS.
As Stu said previously though, there's no good reason for you to do this. In fact, you can use Latitude Docks with your Laptop now (which cost much less than Inspiron ones).