boot into Mac and open terminal:
fdisk -e /dev/disk0
p
f X (X= partition Chameleon is installed to)
w
y
q
That makes the Mac partition active, so you see Chameleon first.
Then boot into XP, right click My Computer, click properties. Click on the Advanced tab, then click on Settings under Startup and Recovery. Under System Startup, click edit and remove the line for Mac from the boot.ini. Save and reboot.