I am definitely not a "sales" type of guy 😉 and usually know nothing about licensing, but people do ask a lot about SCCM pricing and licensing so I needed to find out.
Basically this is the link you want to read: http://www.microsoft.com/systemcenter/configmgr/howtobuy/default.mspx.
However there are a few FAQs not answered by that URL:
Q: Is there an SCCM server license needed for secondary site server?
A: No, "The advantages of using secondary sites are that they require no additional Configuration Manager 2007 server license and do not require the overhead of maintaining an additional database.". See: http://technet.microsoft.com/en-us/library/bb632547.aspx
Q: OK, do I need a client license then on the secondary site server?
A: No, you do not need to install an SCCM client on the SCCM secondary site (and hence don't need an SCCM CAL)
Q: What is the difference in Standard and Enterprise ML for servers?
A: Standard includes SCCM functionality except for DCM for workloads other then Base OS, file&print, networking. And it can only be used on a single installation per-physical machine. That does not apply to Enterprise ML: full workload DCM and can be used to manage any number of OS installations on a single physical server.
For System Center Server suite bundles see: http://www.microsoft.com/systemcenter/svrmgmtsuites/howtobuy/default.mspx
Q: Can I use the Client ML on server OSes?
Q: Do I need the Client ML for each of my client OSes?
A: Only if that client OS does not have a Core CAL, which is rare for large customers: http://www.microsoft.com/calsuites/core.mspx.