When you tag something in gmail, it creates an imap folder. create a personal folder for the emails to be archived then drag and drop the tagged folder using the right mouse button into a subfolder within the personal folder. Create a folder first as for some reason you cannot drag/drop into the root folder structure. Make sure that when you use the right mouse button to drag and drop, you select copy when you let go of the mouse button on the extra menu that appears under the mouse. Be patient with tagged folders over 500 as these will take a while, and outlook will appear to hang. Eventually you will get a progress meter.
The key thing to remember is by default outlook moves when you drag and drop, and if anything goes wrong during this you can lose emails. If you copy, this won't happen.