Debian 6.0 onwards on amd64 and i386 uses the grub-pc (Grub 2) boot loader by default. It's large and over complicated if you only want to boot a single operating system. Changing to the simpler grub-legacy can be done with the following commands:
apt-get --purge remove grub-pc apt-get install grub-legacy grub-install /dev/sda update-grub