Mysql - Max(concat()) Can anyone explain

Hi,

I needed to take the ,"The Rows Holding the Group-wise Maximum of a Certain Field"

I can use subqueries but it is supported after 4.1
Xisto has only 4.0.27.
So no subqueries.

Also you may use a TEMPORARY TABLE.But it is insecure(I am still waiting for a reply in the topic I posted).

Now i found a new way.
MAX(CONCAT) Trick they say.
But i cant understand it.Please explain.

The link to the example and the QUERY :
http://forums.xisto.com/no_longer_exists/

Please help me.
It is going over my head.
The ADMINS must be knowing about this.