This thread is more then 2 years old. I suggest you post your question in the ImpEx forum on vb.com.
That's really not nice or helpful, Marco. In a post dated 1/4/2007 replying to a thread about this exact topic, "custom user fields" on, as you say, the Impex forum on vb.com Steve Machol, customer support manager, says that because the topic "involves rewriting the code" that we should, "please try asking over at vbulletin.org."
Now it turns out that if you come over here, as instructed by Mr. Machol, and search for "customer user threads", then this very thread comes up as number one in the list.
The least that your non-reply is, is not helpful. You could at least have the courtesy to point to an answer. If you don't have something helpful to say, just don't say anything at all. The worst that it is, is unkind and impolite. It certainly does not qualify as user support.