someone correct me if i am wrong but i dont think you can do a full install then revert back to an old 1.6.1 database, well you can but i dont think it will work, you can try to change the setting in your config to point to the old database but the way i see it, 1.7 's db structure is quite different in how it processes.  so im not sure if it will work..    i did a full install in my test area last night but i will try to do the upgrade today sometime and see how it goes...  i dont even think that importing your old db to the new db will work, it might... mmmm...  you might have to just get thru the upgrade somehow...   i will try to import my old one to the new full install empty db and see how it goes today,  unless of course someone already has tried that or knows def one way or the other.