it is not related to your issue at the moment still no harm in knowing it.it seems that by default ping is disabled on windows 8 default firewall configuration & there is a way to enable it without disabling the firewall.
How to Enable Ping Echo Replies in Windows 8 - How-To Geek
now coming to issue at hand i suspect that xp can not access windows 8 shared folders because of incorrect sharing settings.make sure that your xp admin account password is not blank.also check that in win 8 network sharing center type is "home" & in advanced setting password protected sharing is enabled which will prompt for your win 8 username/password when accessing from xp.