Hmm, I think PHP 5 does support mbstring. Look in the php.ini file and check out the php.ini example at
http://www.php.net/manual/en/ref.mbstring.php
Not sure what manual you were reading: The mb_eregi function was experimental, but
php.net now says the following FWIW:
mb_eregi
(PHP 4 >= 4.2.0)
mb_eregi -- Regular expression match ignoring case with multibyte support
Description
int mb_eregi ( string pattern, string string [, array regs] )
mb_eregi() executes the regular expression match with multibyte support, and returns 1 if matches are found. This function ignore case. If the optional third parameter was specified, the function returns the byte length of matched part, and the array regs will contain the substring of matched string. The functions returns 1 if it matches with the empty string. If no matches found or error happend, FALSE will be returned.
The internal encoding or the character encoding specified in mb_regex_encoding() will be used as character encoding.
See also: mb_regex_encoding(), mb_ereg().
Other posts have indicated a possible issue with PhpDig 1.8.8 RC1 running on PHP 5, but I'm not yet sure if this is related to php.ini settings or whether some PhpDig code needs reworking.