This would be a common question when trying to figure out licensing compliance in the corporate world!:-) Usually when folks are looking for information about processors, they're probably also interested in the number of cores too!
Generally, the manufacturer--DELL, HP, etc. have managment tools on board that get you close--but the best tool out there that I know of for answering the "how many processors" and "how much core" question(s) is something called SIW (System Information for Hardware) . 
There's a free version available http://www.gtopala.com -- but -- it really is for home use. If you're a corporate sys admin (READ: the latest version of the tool will figure that out by your hardware config) or a technician working on corporate class boxes, the commercial versions of the product are available at a reasonable cost (e.g. tech lic: < $100.00). The links below are direct download connections for the 30-Day trail copies.
Business Class:
http://www.regnow.com/trialware/download/Download_siwb.exe?item=14479-2&affiliate=278047
Tech Class:
http://www.regnow.com/trialware/download/Download_siwt.exe?item=14479-1&affiliate=278047