I think you should should manually edit your /boot/grub/grub.conf file to boot your operating systems using grub.
Here i am assuming that your winXP is on first drive first partition.. ie. hd (0,0) and linux is on second drive first partition.. ie. hd (1,0)
Now your grub.conf should look like this.
default=windows
timeout=10
color=green/black light-gray/blue
# winXP loading
title windows
rootnoverify (hd0,0)
chainloader +1
# section to load linux
title linux
root (hd1,0)
kernel /vmlinuz root=/dev/hdb1
boot