In the new web page for SharePoint for MOSS there is couple of pages that explains it in detail. I recommend you to review the FAQ page that resolves the common doubts in MOSS licensing:
http://sharepoint.microsoft.com/how-to-buy/Pages/licensing-overview.aspx
http://sharepoint.microsoft.com/how-to-buy/Pages/faq.aspx
These tables represent the license model as I understand it. I recommend that you take it as guidance and check it with your license provider or Microsoft representative.
Products
Product | Public price | Features | CAL Requirements |
WSS | Free. Included in W2K3 license. | Basic collaboration | Review the W2K3 CAL requirements. Needs the External Connector for non-employees. |
Microsoft Office SharePoint Server 2007, Server License | $4,424 | Full equip for users with enterprise CAL. Standard CAL does not include: BDC, Excel Services, Forms Services, Business Intelligence, Forms Server. | Only for employees. Each employee needs a Std. or Ent. CAL |
Microsoft Office SharePoint Server 2007 for Internet sites | $40,943 | Full equip | Non-employees don't need any CAL. Each employee needs a Std. or Ent. CAL |
Microsoft Office SharePoint Server 2007 for Search (Enterprise Edition), Server License | $57,670 | Full equip | Only for employees. No need any CAL. * Seems that this product is no longer available. |
Microsoft Office SharePoint Server 2007 for Search (Standard Edition), Server License | $8,213 | Not included: BDC, Excel Services, Forms Services, Business Intelligence, Forms Server. Index limited to 500.000 documents. | Only for employees. No need any CAL. Recommended for +40 standard CALs. |
Microsoft Forms Server 2007, Server License | $4,424 | Only forms | Only for employees. Each employee needs a Forms CAL |
Microsoft Forms Server 2007 for Internet sites | $22,118 | Only forms | Non-employees don't need any CAL. Each employee needs a Std. or Ent. CAL |
Search Server Express | Free | All Enterprise Search features except BDC Search and limited to only one server. Not scalable. | No need any CAL. |
Search Server | Not public? | All Enterprise Search features except BDC Search. | No need any CAL. |
Update 05/06/2009: Seems that "Microsoft Office SharePoint Server 2007 for Search (Enterprise Edition), Server License" is no longer available and then you need to purchase a CAL for each user inside the organization.
Client Access License (CAL)
Each SharePoint CAL needs a SQL Server CAL if SQL Server is not licensed per server. The same is applicable to Windows 2003 Server.
Product | Public price | Features |
Office SharePoint Server 2007 Standard CAL | $94 | Not included: BDC, Excel Services, Forms Services, Business Intelligence. |
Office SharePoint Server 2007 Enterprise CAL | $75 | Full Equip and needs an Office SharePoint Server 2007 Standard CAL ($94) |
Office Forms Server 2007 CAL | $54 | Only forms |
Office SharePoint Designer 2007 | Free (since April 2009) | The tool to customize SharePoint 2007. |
All information has extracted from Office official page: