This is great read at Redmond Magazine (previous MCP Magazine). You get some overview on licensing (if you are not into reading the lengthy licensing guides at Microsoft website). Then you get a drilldown on cost saving when negotiating software licenses.
http://redmondmag.com/features/article.asp?editorialsID=441 (the article)
http://www.microsoft.com/licensing/default.mspx (Microsoft Licensing WebSite)