I've just bought my VPS from KnownHost (very good service so far) and I'm wanting to set it up similar to a reseller so that all my domains share the IPs that I have been provided with, rather then each one taking a single IP. My VPS has WHM/cPanel on it so if you have experience doing what I want, please shoot me a PM, there may even be a financial reward, or a free blog post on my blog, if your help is useful to me.
When you go to WHM >> Create new account and you fill the form, there is a checkbox that makes the domain take its own IP. If its unchecked, the domain will be assigned to the main shared IP.