I would backup your grub config file, and try this one in its place:

Code:
default		0
timeout		10

title		Ubuntu, kernel 2.6.10-5-386 
root		(hd0,2)
kernel		/vmlinuz-2.6.10-5-386 root=/dev/hda5 ro
initrd		/initrd.img-2.6.10-5-386

title		Microsoft Windows XP Professional
root		(hd0,0)
makeactive
chainloader	+1