When ordering your plan, select the 'I have a domain and will update my nameservers' option on the order form, and enter the domain name you will use on the 2nd page. You must then ask the people you registered the domain with in the first place to point the domain to our names servers:
ns1.dadshosting.com
ns2.dadshosting.com
This process can take some time, namely the time it takes your registrar to update it, plus 24-48 hours on average to propogate round the world's DNS servers (see 'Why doesn't my domain work straight away?)
