If you are doing internet connection sharing from the XP box, your OS9 comptuer will be able to connect just fine. You will need to put the OS9 box in the same IP range as the port you are connecting to on the XP box. This will only work if the XP box has 2 network connections (2 ethernet, or 1 ethernet, and 1 Wireless).
I use Microsoft internet connection sharing on my Dell laptop to connect my OLD Macintosh LC computer to the internet. Since the Laptop is Wireless, and has a normal Ethernet connection also, I connect the LC to the Ethernet port on the laptop, and share my Wireless internet connection on the Dell with the LC.
IT is the easiest way to make an old Macintosh Wifi compatible