一般装XP+ubuntu双系统并且在没有修改引导菜单的话
在开机后grub启动后，会有类似于以下几个引导条（我的是8.04 beta版）：
Ubuntu hardy (development branch)
Ubuntu hardy (development branch), kernel 2.6.24-12-generic (recovery mode)
Ubuntu hardy (development branch), memtest86+
Other operating systems:
Microsoft Windows XP Professional
并且默认是在上面数下来第一个
下面说如何修改这个菜单吧，进入ubuntu系统后，打开终端执行：
sudo gedit /boot/grub/menu.lst
执行次命令后，默认的menu.lst是这样的：
# menu.lst – See: grub(8), info grub, update-grub(8)
# grub-install(8), grub-floppy(8),
# grub-md5-crypt, /usr/share/doc/grub
# and /usr/share/doc/grub-doc/.
## default num
# Set the default entry to the entry number NUM. Numbering starts from 0, and
# the entry number 0 is the default if the command is not used.
#
# You can specify ’saved’ instead of a number. In this case, the default entry
# is the entry saved with the command ’savedefault’.
# WARNING: If you are using dmraid do not use ’savedefault’ or your
# array will desync and will not let you boot your system.
default 0
## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout 8
## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu
# Pretty colours
#color cyan/blue white/blue
## password ['--md5'] passwd
# If used in the first section of a menu file, disable all interactive editing
# control (menu entry editor and command-line) and entries protected by the
# command ‘lock’
# e.g. password topsecret
# password –md5 $1$gLhU0/$aW78kHK1QfV3P2b2znUoe/
# password topsecret
#
# examples
#
# title Windows 95/98/NT/2000
# root (hd0,0)
# makeactive
# chainloader +1
#
# title Linux
# root (hd0,1)
# kernel /vmlinuz root=/dev/hda2 ro
#
#
# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST
### BEGIN AUTOMAGIC KERNELS LIST
## lines between the AUTOMAGIC KERNELS LIST markers will be modified
## by the debian update-grub script except for the default options below
## DO NOT UNCOMMENT THEM, Just edit them to your needs
## ## Start Default Options ##
## default kernel options
## default kernel options for automagic boot options
## If you want special options for specific kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
## kopt_2_6_8=root=/dev/hdc1 ro
## kopt_2_6_8_2_686=root=/dev/hdc2 ro
# kopt=root=UUID=a17564ff-c85d-42b7-ac2e-5798d7e209ab ro
## Setup crashdump menu entries
## e.g. crashdump=1
# crashdump=0
## default grub root device
## e.g. groot=(hd0,0)
# groot=(hd0,8)
## should update-grub create alternative automagic boot options
## e.g. alternative=true
## alternative=false
# alternative=true
## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
## lockalternative=false
# lockalternative=false
## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet splash
## should update-grub lock old automagic boot options
## e.g. lockold=false
## lockold=true
# lockold=false
## Xen hypervisor options to use with the default Xen boot option
# xenhopt=
## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0
## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
## altoptions=(recovery) single
# altoptions=(recovery mode) single
## controls how many kernels should be put into the menu.lst
## only counts the first occurence of a kernel, not the
## alternative kernel options
## e.g. howmany=all
## howmany=7
# howmany=all
## should update-grub create memtest86 boot option
## e.g. memtest86=true
## memtest86=false
# memtest86=true
## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false
## should update-grub add savedefault to the default options
## can be true or false
# savedefault=false
## ## End Default Options ##
title Ubuntu hardy (development branch)
root (hd0,8)
kernel /boot/vmlinuz-2.6.24-12-generic root=UUID=a17564ff-c85d-42b7-ac2e-5798d7e209ab ro quiet splash
initrd /boot/initrd.img-2.6.24-12-generic
quiet
title Ubuntu hardy (development branch), kernel 2.6.24-12-generic (recovery mode)
root (hd0,8)
kernel /boot/vmlinuz-2.6.24-12-generic root=UUID=a17564ff-c85d-42b7-ac2e-5798d7e209ab ro single
initrd /boot/initrd.img-2.6.24-12-generic
title Ubuntu hardy (development branch), memtest86+
root (hd0,8)
kernel /boot/memtest86+.bin
quiet
### END DEBIAN AUTOMAGIC KERNELS LIST
# This is a divider, added to separate the menu items below from the Debian
# ones.
title Other operating systems:
root
# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/sda1
title Microsoft Windows XP Professional
root (hd0,0)
savedefault
makeactive
chainloader +1
刚开机看到系统引导菜单时，显示的那几个选择项就是menu.lst里面后边部分的前面带有“title”的那一行
在前面的内容中“default 0”后面的数值0是第一个选择项，如果分别改成1、2、3、4的话，则分别把默认启动的选择项放在第二、三、四、五个选择项上面。“timeout 8”后面的数值8则表示选择引导条的默认倒计时为8秒，当然，这个数值可以改得更大，比如20、30什么的，不过如果把数值改成负1，即“-1”的话，在开机看到grub选择项时没有倒计时，直到选择了所要启动的引导条并回车才能进入系统
每一行的前面加一个“#”号表示把那一行注释掉，比如说我把启动菜单的一些非必要的引导条（以下3个）注释掉：
Ubuntu hardy (development branch), kernel 2.6.24-12-generic (recovery mode)
Ubuntu hardy (development branch), memtest86+
Other operating systems:
注释掉之后，剩下了如下的两个引导条：
Ubuntu hardy (development branch)
Microsoft Windows XP Professional
上面的UBUNTU对应的default后面的数值则为”0”，如果要改成默认XP启动的话，则把default后面的数值改为”1“ (如果没有注释掉那3个引导条，而又要默认XP启动的话，则把此数值改为”4″即可)
P.S：修改了menu.lst文件并确认没改错的话，先保存再关闭，重启系统，即可看到修改之后的内容