check if a name seems "human"?

I would recommend concentrating your energy on building a user interface that makes it brain-dead easy to list all new names to an administrator, and a big fat "force to rename" mechanism that minimizes the admin's workload, rather than trying to define the incredibly complex and varied rules that make a name (and program a regular expression to match them!).

Update - one thing comes to mind, though: Second Life used to allow you to freely specify a first name (maybe they check against a database of first names, I don't know) and then gives you a selection of a few hundred pre-defined last names to choose from. For an online RPG, that may already be enough.

You could use a metaphone implementation and then look for "unnatural" patterns:

http://www.php.net/manual/en/function.metaphone.php

This is the PHP function for metaphone string generation. You pass in a string and it returns the phonetic representation of the text. You could, in theory, pass a large number of "human" names and then store a database of valid combinations of phonemes. To test a questionable name, just see if the combinations of phonemes are in the database.

Hope this helps!

Would limiting the amount of consonants or vowels in a row, and preventing repeating help?As a regex:

if(preg_match('/[bcdfghjklmnpqrtsvwxyz]{4}|[aeiou]{4}|([a-z])\1{2}/i',$name)){    //reject}

Possibly use iconv with ASCII//TRANSLIT if you allow accentuated characters.