You SHOULD be able to install 3.318 and run it.
You purchased Hoster on May 22, 2006, which is after the March 30, 2006 requirement date.
Download the correct file for Hoster 3.318 from:
http://www.mtu.com/upgrades/hoster.htm
Make sure you are using the same RegCode you did with your 3.317 install.
Post back here whether you fail or succeed to install so we know.