The only way to get it on a 7200 is by replacing certain parts of your 9.1 System folder with the 9.2.1 parts. You can't actually get a full 9.2.1 system on that computer. It would be kind of a 9.1/9.2.1 hybrid system. I really don't think it's worth it. Most of the updates from 9.1 to 9.2.1 were for better compatability with OS X.