update 2 ip address

No. Each Dynamic DNS hostname can only have a single IP address. With Custom DNS you can have multiple IP addresses, but you can't update them with an update client.

I take it you're trying to do some form of load balancing or similar?

thanks for the reply. yes thats right so how would i keep this up to date if the ip adresses change

You may find that creating 2 hosts (eg alpha.example.com and beta.example.com) and then setting up your main host with those as CNAMEs:

www.example.com    CNAME    alpha.example.com.
www.example.com    CNAME    beta.example.com.

does what you're after. I don't know if DynDNS support that though.

thanks again if dyndns dont support that is there any where that i can set it up thanks again for your reply you have been very helpfull

The first thing to do is to try it. Unfortunately if it doesn't work I don't know what other, low cost, solution there is - particularly as you haven't said what you're actually trying to do ;)

ok will try to explain i have 2 servers that are at seperate locations which have individual free dns acounts which each have 2 host names and when 1 of these servers go down due to internet failure or power problems which ive been having im looking to re-direct the traffic from the server thats is down to the server which is fine

Ah, you want failover. Then you can certainly do that yourself, though it comes with some risks - if your 2 sites can't see each other, but both otherwise have connectivity to the Internet they'll update the hostname as if they remote site had failed, effectively swapping the hostnames over.

You'll need some form of service monitoring software (your choice, but Xymon may be worth a look) on each site. You'll have to set it up to monitor the other site and to run a script on service failure and recovery. That script will then be responsible for performing the update - probably using your existing update client, but with a different configuration file. It will also have to kill the update daemon when the service has recovered.

Doing this on Linux or BSD will be relatively simple, doing it on Windows will be more complicated, but not impossible.

thanks again for your reply had a look on xymon and just got confused ive been looking at secondary dns maybe this will work for me

No, Secondary DNS won't do what you're after - that is for use with your own domain where you already have a single DNS server. The only DynDNS service that will do this is the full Dynect platform - that is not a low cost solution.