As you can ping host from the guest, it tells that the connection is working ok both ways (response comes back ok). The problem probably is that XP has not been configured to answer to ping requests so it's silently discarding them. You need to change the settings of the firewall to allow answers to ping.
See for example http://kb.iu.edu/data/aopy.html for details how to enable ping service in different Windows versions with the default firewall.