By default, XP Mode uses Virtual PC NAT, using its own IP addresses outside your home network (image 1). To change it, you have to change XP Mode network settings to use your host's NIC (image 2).
To do this, turn off the XP Mode (do not hibernate). Change the settings, click OK, reboot your host and start XP Mode.
Should work now.
Kari
Image 1:
Image 2: