Generate dynamic answers from bind 8.2.x

[Piet Honkoop]

In order to create a fully redundant setup for a server set, we are looking
for a possibility to dynamically generate an answer if a request for a certain
A record comes in (www.domain.com). The answer will be depending on a number
of factors:
	* source of the request (the DNS server will have access to a full
	  BGP table)
	* load of the nearby servers (so that weighted load balancing can
	  take place over the various servers).
	* availability of the server(s)

Needless to say, the servers will be spread around the world and by dynamically
answering to DNS requests we try to keep the traffic localized as much as 
possible.

My questions:
	* does such a setup exist? If so, where can we find info about this
	* if not, how difficult is it to implement this (for an experienced
	  C programmer without in-depth knowledge of BIND sources)

Thanks,

Piet