As with other tools released with SMS, you should only use tools that are either designed, or supported, for the specific product version you are installing. The Capacity Planning tool released for SMS 2003 SP1 should not be used to determine a capacity planning baseline for Configuration Manager 2007 site installations. The tool results should also be used only as very general guidance when used to determine capacity planning requirements for sites running SMS 2003 SP2 or SMS 2003 SP3 as the tool was not designed to consider post-SP1 features (OSDFP, DMFTP, AI, etc...).
Because the Capacity Planning tool released for SMS 2003 SP1 is not compatible with Configuration Manager 2007, it should not be used to determine suggested site capacity planning requirements for Configuration Manager 2007 sites. When the SMS 2003 Capacity Planning tool was developed, it was not designed to consider SUM, DCM, OSD, and many other changes (and new features) that were added in Configuration Manager. If you plan to deploy many of these new features you may require additional hardware, system resources, and network bandwidth above and beyond those required for SMS 2003 sites.
If you are planning to deploy Configuration Manager in a very large or complex environment (with hundreds of thousands of clients, or with thousands of packages, or with shorter policy polling intervals, etc...), you must plan to scale your resources accordingly. For example, when scaling capacity planning for a large site in a network bandwidth sensitive environment, not only software distribution package download should be carefully planned for, but you should also research and plan for the network bandwidth used for large volumes of: client policy downloads, inventory data reports, and large volumes of status and state messages.
There isn't a Capacity Planning tool released for Configuration Manager as of right now. However, the Configuration Manager help topic Configuration Manager Site Capacity Planning gives some general recommendations that can be used as a baseline to help determine site capacity planning information that is appropriate to your organization. This information is provided as general guidance only, because actual site capacity requirements will vary depending on factors such as the hardware used to host Configuration Manager site systems, your specific network environment, how many clients you will support, and how Configuration Manager features and client agents are implemented to support your business and technical objectives.