As already stated in a dozen places. You must use the everquest2.exe with the matching date and build that the extension is developed for. Each time SoE forces us to patch (95% of all patches are not forced), you must patch the day forced then wait for an extension.
As a new user, you must wait for the next forced patch to get your files in sync, or you can look at the eq2 archives on
http://isxeq2.twonk.net/. Remember these archives are independently maintained. And while much of the time the link on the main page with the currently supported version is correct, some times (like last I looked it is not).
You're in luck, cause you atleast speak read the english language and can clearly discern the date on the isxeq2 (20070328), and you can click the archives link on twonk and look thru the list till you find 200703280700 (March 28th, 2007 7:00 am). Like magic, when using the files from the correct dates, the extension works and you can begin your path to nirvana.
But I'm sure you read the resources Ama pointed you to that already have this listed atleast a dozen times, and you found the half dozen references to the live irc channel that answers these questions frequently.