There is probably a backdoor password that will get you into BIOS (so then you can remove the current bios password). Call Dell tech support and ask for it. I think I know what it is but I don't feel like it's a good idea to publish it on the forums. If Dell won't give you the password, send me a message and I'll give you one you can try.
Removing the button cell battery should work. You have to leave it out for 5 minutes or so and you the system has to be totally unplugged (no battery or AC power or anything)