Help in grub config

[João Guilherme Sauer]

Hi Guys,

I would like to changemy grub to enter only when I press the F12
button. If this key is not pressed, the grub will enter in the linux.
So, here is my menu.lst:
**************************************************
default=0
timeout=5
splashimage=(hd0,2)/boot/grub/splash.xpm.gz

title Red Hat Linux
        root (hd0,2)
        kernel /boot/vmlinuz-2.4.20-8sysemu ro root=LABEL=/ hdc=ide-scsi
        initrd /boot/initrd-2.4.20-8.img

title Windows XP
        root (hd0,0)
        chainloader +1
        makeactive
 **************************************************
So, explain again:
1- If I don't press F12 key, I would like that the grub select the default;
2- If I press F12 key, I would like that the grub select the other option.

I know that is possible to assign the F12 to enter command, but by
this way, I will go enter in the default option and not in the other
option.

How I can do this?

thanks a lot,
João