XP as default boot How?

[nebtem]

If you in root shell, just enter:
vim /boot/grub/menu.lst
or
nvi /boot/grub/menu.lst

vim or nvi is editor on command prompt

I did this and I get nothing. I now know why I use XP. This is very difficult. All I weant to do is to change the default to saved (last system loaded) or the XP as default system Me and my family use XP all the time but I want to try linux and work with it so I only want it to load when directed not as default. There must be a way to do this. I can see what I have to do but I can not get it done
what my system has:

# menu.lst - See: grub(, info grub, update-grub(
# grub-install(, grub-floppy(,
# 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'.
default 0

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout 5


What I want:

# menu.lst - See: grub(, info grub, update-grub(
# grub-install(, grub-floppy(,
# 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'.
default saved

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout 10

But my system will not allow me to save any changes to the file