Dell provides Ubuntu support for updating the BIOS of Dell systems:

http://direct2dell.com/one2one/archive/2007/12/05/37446.aspx

… be sure the Universe section is enabled in /etc/apt/sources.list, then run as root:

wget -q -O – http://linux.dell.com/repo/firmware/bootstrap.cgi | bash
aptitude install firmware-addon-dell
aptitude install $(bootstrap_firmware -a)
update_firmware

Thanks Dell!