This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The latest version of struts (1.3.5) is the easiest to tell, because finally they started putting the version number as part of the jar file names.
With the earlier versions, it's a bit harder. The best way I know of to tell is to download a specific version of Struts and compare the last-modified date of the struts.jar file in that version with the last-modified date of the one you're using.