I use a german version of windows 2000 for testing.

perf_counter[\Speicher\Verfügbare Bytes]

will not be accepted in the webinterface. If you insert it into the database directly everything works fine.

A quickfix would be turning input validation off, which is NOT the fix for the future ,)

see defines.inc.php
change from:
define('ZBX_EREG_PARAMS', '([[:print:]]+)

{0,1}');

to:
define('ZBX_EREG_PARAMS', '(.+){0,1}

');