which resides under /boot/grub directory.
boot screen will look like this...
and each options are numbered from 0 to n( 7 here )
Ubuntu,with linux 2.6.35-23-generic =0
Ubuntu,with linux 2.6.35-23-generic(recovery mode)=1
Ubuntu,with linux 2.6.35-22-generic =2
Ubuntu,with linux 2.6.35-22-generic(recovery mode)=3
Memory test (memtest86+) =4
Memory test(memtest86+,serial console 115200) =5
Windows Vista (loader) (on /dev/sda1) =6
Windows Vista (loader) (on /dev/sda2) =7
now in grub.cfg file set default="7" to keep default boot windows vista
and to keep ubuntu as default boot