These are all group policy settings
They have been set by your administrators. It's also not one server with this option set, but all the domain controllers in your domain. They replicate these settings between each other and are responsible for authentication when you log in to the network.
Viewing Group Policy
You can take a look at group policy by opening Group Policy Management. It's unlikely that it's installed on your machine, but if you have permissions to install programs you could install RSAT, though I'm not sure you'd want IT to catch you doing this as it could be misconstrued as malcious.
I was surprised to find this on our terminal server (or Remote Desktop Server for you pedants out there.) I logged in as a random user whose password I happen to know and voila, I could see all our group policy objects and inspect their settings.
What you're looking for is the Default Domain Policy. Drill down in to Windows Settings, Security Settings, and Account Policies/Password Policy and you'll be able to see the password settings:
Keeping the old password
There probably isn't a way for you to keep your old password. On second thought, you don't mention password history. If there is no password history, change your password and then change again to the old one. You really should just man up and learn the new one though. If there are no complexity requirements, try using a few words instead of strange subsititions.