what is really happening???? win xp pro issue

i have this piculier problem.

usually i used to ping by just typing

ping 192.168.0.10

now when i do so, it displays an error message stating that:

"c:\WINDWOS\system32\ping.com is not a valid Win32 application"

from where has this ping.com come from????

but i can make use of it by typing ping.exe 192.168.0.10


also,

if i type regedit, it states that this
"regedit is not a valid Win32 appliaction"

whereas if i type regedit.exe, it works. sounds mysterious????!!!!

anyone out there having solution for my query?????