My config :
Existing Dual boot XP & Ubuntu managed by GRUB

Installing Backtrack 4 on Grub is quite similar to the Lilo one:

1) Make a ext3 partition via Hiren's boot cd or any boot partition utility
2) Format it via this same utility
3) Boot BT4 beta
4) Once loggued open a terminal and :

take your partition freshly formated let's say in this case /dev/sda7
( you can also do a root@bt:~#df -h to see if it's the right one ... )
root@bt:~#umount /dev/sda7
root@bt:~#cd / && mkdir /mnt/bt && mount /dev/sda7 /mnt/bt/
root@bt:~#cp --preserve -R /{bin,dev,home,pentest,root,usr,boot,etc,lib,opt,sb in,var} /mnt/bt/ && mkdir /mnt/bt/{mnt,tmp,proc,sys}
root@bt:~#chmod 1777 /mnt/bt/tmp/ && mount -t proc proc /mnt/bt/proc && mount -o bind /dev /mnt/bt/dev/
root@bt:~#chroot /mnt/bt/ /bin/bash

Now Bt4 beta is copied on /dev/sda7 we need to add it on GRUB so reboot your machine under ubuntu, open a terminal and:
root@ubuntu:~#grub-install /dev/sda7
root@ubuntu:~#vim /boot/grub/menu.lst
At the end of the file add :

title Backtrack 4 Beta
root (hd0,6)
kernel /boot/vmlinuz rw root=/dev/sda7
initrd /boot/splash.initrd

root@ubuntu:~#update-grub && reboot

You should be able to boot your Backtrack beta 4 now