Which CAL you need is going to depend on the server edition as well as the features you will you will be accessing.

For WSS you are not going to need a server CAL or user CAL’s –it’s completely free and can be downloaded from Microsoft’s website

http://technet.microsoft.com/en-us/windowsserver/sharepoint/bb400747.aspx

If you are Running MOSS 2007 you will need a CAL for each computer Accessing the server.  If you are using Enterprise features you must purchase an Enterprise CAL in addition to the Standard CAL.

For MOSS 2007 for internet sites, MOSS 2007 for Search Enterprise Edition, and MOSS 2007 for Search Standard Edition a CAL is not required.  Each is licensed per server and does not require client access licenses.

For Office Forms Server a Forms CAL must be purchased for each client computer accessing the server.

The Standard Cal will allow clients to access the portal, personalization, search, and enterprise content management features.

The Enterprise CAL will allow you to use the business process integration and business intelligence features, including Report Center, Excel Services, Business Data Catalog and InfoPath Forms Services.