CharToLower only works on single characters. As Wyon said, StrEqual has an optional argument that you can set to false to do a case-insensitive comparison (i.e. it will consider "HELP", "help", "hElP", etc... to be equal).
Actually, that reminds me, I wonder if the doc creator will ever be updated to show the default values of optional arguments. The actual signature for StrEqual is
PHP Code:
stock bool StrEqual(const char[] str1, const char[] str2, bool caseSensitive=true)
but the "=true" is missing from the documentation page for it.