The Pathway to the Solution
I thought I would blog about this as I personally found it quite complex to begin with. The Solutions Pathway is a way of saving money if you are migrating from a previous version of a product in the Windows Essential Server Solutions umbrella to a newer version (see below).
The website: http://www.microsoft.com/sbs/en/us/upgrade.aspx
At the bottom click continue, and there is a agreement that needs accepting on the next page. On the page after you will see this:

Once processed you are given the options you can migrate to:
You are then presented with a discounted purchase list for the Product you chose and the relevant and CALs. Below is both SBS 2008 standard (from SBS 2003 standard) and EBS 2008 standard (from SBS 2003 standard):
Please note these prices are current for 03/04/2008 in the UK only and may be subject to change.

Proceed to the checkout and Job done :D