Your ISP will not normally update DNS records on your request for your domain name.
However, for those of you that don't want to wait the normal 24-48 hours, there are some temporary solutions you can try in order to enable you to access your website via your domain name whilst waiting for DNS propagation.
Before you do any of the below, please ensure you make notes of any settings you change in your environment and only attempt to make these changes if you are technically confident.
a) Place a static entry into your operating system DNS host file pointing to your domain and new IP. Your web server IP address is detailed in the 'Welcome' email you receive during sign up. On Windows the host file can normally be found at:
c:\winnt\system32\drivers\etc\hosts, or at c:\windows\system32\drivers\etc\hosts
or
b) Set your computer, router or modem to use alternative DNS servers (a little more tricky).
After a couple of days, make sure you set things back to the way they were previously.
