I have recently moved one of my own domain to a new server with my UK based ISP. It does take time for the DNS settings to be propagated throughout the internet. It can take 24 to 36 hours for the DNS propagation to complete. I found a useful tool whereby you can check the status of the DNS propagation at different locations of the world by accessing the following url.

http://www.preshweb.co.uk/cgi-bin/dns-propagation-tracker.pl

Just enter your domain name at the box and press "enter".

from prompt type the following;

nslookup www.(site_name). That will return the IP.