php.ini настраивать надо скорее всего.
Там есть такие опции, как включение _POST, _GET, _HTTP_GET_VARS
Добавлено спустя 1 минуту 2 секунды:
+ register_globals On
проверь
; You should do your best to write your scripts so that they do not require
; register_globals to be on; Using form variables as globals can easily lead
; to possible security problems, if the code is not very well thought of.
register_globals = On
; Whether or not to register the old-style input arrays, HTTP_GET_VARS
; and friends. If you're not using them, it's recommended to turn them off,
; for performance reasons.
register_long_arrays = On
; This directive tells PHP whether to declare the argv&argc variables (that
; would contain the GET information). If you don't use these variables, you
; should turn it off for increased performance.
register_argc_argv = On
; When enabled, the SERVER and ENV variables are created when they're first
; used (Just In Time) instead of when the script starts. If these variables
; are not used within a script, having this directive on will result in a
; performance gain. The PHP directives register_globals, register_long_arrays,
; and register_argc_argv must be disabled for this directive to have any affect.
auto_globals_jit = On