When you add a domain to your account a DNS Zone is created on our DNS Servers, this zone will contain around 10 to 15 IP address for things like website, mail servers, MX Records, webmail, statistics service, control panel, and others.
The IP address for the website would be a shared IP address for which ever of our web servers your website is assigned to. Websites do not need to have a static IP address unless you require it for a secure SSL connection.
If you did wish to have a Static IP address for your website this can be purchased from your Client Area account, however unless you had a specific reason for wanting one there is no reason to have one.
If you wished to have a static IP address to view a website before pointing the domain at our network (updating the nameservers) then you do not need to with our systems as when you add a domain to your account a second 'instant alias' domain is created. This 'instant alias' domain can be used for testing the website before pointing the domain at our network.