Ping missing on both systems?
ping.exe should be located in the c:\windows\system32 directory. Try typing
c:\windows\system32\ping.exe 192.168.n.n
If that works then you path string has got snafued somehow. If ping.exe is missing :O
Found this MS document that might help - if you can get ping working!
http://support.microsoft.com/?scid=kb;EN-US;Q308007