You parse the XML and store it in a database. Right now I have the last 5 months of my guilds bank logs stored in a database and the page for viewing them has many of the features of the armory with a few other options for sorting and displaying it added.

Actually the above scripts main purpose will be to allow administrators to log in and update the stored data as often as needed without needing know anything more than their WoW loging info.

On a side note if your just looking to have your browser hold the data you can set up you browser to store websites for use offline. Of course if the armory is just slow to get that data you will need to disconnect your PC from your ISP for it to work.