per avere tutti i SO indipendenti , sia windows 7 che XP li devi installare su unità diverse , mantenendo attiva nel bios la sola unità dove esegui l' installazione , in tal modo sia l' uno che l' altro installano il solo proprio bootloader sul MBR della propria unità , poiche essendo tutte le altre disattivate non vengono rilevate.
Sul mio desktopo hardisch ne ho tre , uno da 80 per xp , uno da 500 per winbu7tee , e uno da 350 per linux , con attualmente 2 distribuzioni installate. (ubuntu Maveric e Debian Squeezy Il tutto tranquillamente gestito da grub di ubuntu collocato sull' unità linux .
Aggiornare grub ogni volta che testo altre distro , è un giochetto da mezzo minuto , il tempo per riavviare da ubuntu e dare un bel update-grub ed è fatta. Inoltre nell' evetualità che ubuntu faccia il co..ne e mi lasci a piedi con il bootloader se ho bisogno immediato di wincozza , mi basta mettere una qualunque delle 2 unità windows come prima unità di boot per ripartire senza problemi

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
set have_grubenv=true
load_env
fi
set default="0"
if [ "${prev_saved_entry}" ]; then
set saved_entry="${prev_saved_entry}"
save_env saved_entry
set prev_saved_entry=
save_env prev_saved_entry
set boot_once=true
fi

function savedefault {
if [ -z "${boot_once}" ]; then
saved_entry="${chosen}"
save_env saved_entry
fi
}

function recordfail {
set recordfail=1
if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}

function load_video {
insmod vbe
insmod vga
}

insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
if loadfont /usr/share/grub/unicode.pf2 ; then
set gfxmode=640x480
load_video
insmod gfxterm
fi
terminal_output gfxterm
insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
set locale_dir=($root)/boot/grub/locale
set lang=it
insmod gettext
if [ "${recordfail}" = 1 ]; then
set timeout=-1
else
set timeout=10
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
menuentry 'Ubuntu, with Linux 2.6.35-25-generic' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
linux /boot/vmlinuz-2.6.35-25-generic root=UUID=3471a938-2e68-443c-99a4-7618c9417bef ro quiet splash
initrd /boot/initrd.img-2.6.35-25-generic
}
menuentry 'Ubuntu, with Linux 2.6.35-25-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
echo 'Loading Linux 2.6.35-25-generic ...'
linux /boot/vmlinuz-2.6.35-25-generic root=UUID=3471a938-2e68-443c-99a4-7618c9417bef ro single
echo 'Loading initial ramdisk ...'
initrd /boot/initrd.img-2.6.35-25-generic
}
menuentry 'Ubuntu, with Linux 2.6.35-22-generic' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
linux /boot/vmlinuz-2.6.35-22-generic root=UUID=3471a938-2e68-443c-99a4-7618c9417bef ro quiet splash
initrd /boot/initrd.img-2.6.35-22-generic
}
menuentry 'Ubuntu, with Linux 2.6.35-22-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
echo 'Loading Linux 2.6.35-22-generic ...'
linux /boot/vmlinuz-2.6.35-22-generic root=UUID=3471a938-2e68-443c-99a4-7618c9417bef ro single
echo 'Loading initial ramdisk ...'
initrd /boot/initrd.img-2.6.35-22-generic
}
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/20_memtest86+ ###
menuentry "Memory test (memtest86+)" {
insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
linux16 /boot/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
insmod part_msdos
insmod ext2
set root='(hd2,msdos1)'
search --no-floppy --fs-uuid --set 3471a938-2e68-443c-99a4-7618c9417bef
linux16 /boot/memtest86+.bin console=ttyS0,115200n8
}
### END /etc/grub.d/20_memtest86+ ###

### BEGIN /etc/grub.d/30_os-prober ###
menuentry "Windows NT/2000/XP (on /dev/sda1)" {
insmod part_msdos
insmod ntfs
set root='(hd0,msdos1)'
search --no-floppy --fs-uuid --set 1e0ce7300ce7021f
drivemap -s (hd0) ${root}
chainloader +1
}
menuentry "Windows 7 (loader) (on /dev/sdb1)" {
insmod part_msdos
insmod ntfs
set root='(hd1,msdos1)'
search --no-floppy --fs-uuid --set 98ceef08ceeedd8e
chainloader +1
}
menuentry "Debian GNU/Linux, with Linux 2.6.32-5-amd64 (on /dev/sdc2)" {
insmod part_msdos
insmod ext2
set root='(hd2,msdos2)'
search --no-floppy --fs-uuid --set 90204dbb-ed6a-4ee7-8c8a-bea7da5ce6f0
linux /boot/vmlinuz-2.6.32-5-amd64 root=UUID=90204dbb-ed6a-4ee7-8c8a-bea7da5ce6f0 ro quiet
initrd /boot/initrd.img-2.6.32-5-amd64
}
menuentry "Debian GNU/Linux, with Linux 2.6.32-5-amd64 (recovery mode) (on /dev/sdc2)" {
insmod part_msdos
insmod ext2
set root='(hd2,msdos2)'
search --no-floppy --fs-uuid --set 90204dbb-ed6a-4ee7-8c8a-bea7da5ce6f0
linux /boot/vmlinuz-2.6.32-5-amd64 root=UUID=90204dbb-ed6a-4ee7-8c8a-bea7da5ce6f0 ro single
initrd /boot/initrd.img-2.6.32-5-amd64
}
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f $prefix/custom.cfg ]; then
source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###