You don't need to upload anything to Picasa once you've downloaded it, just add your existing folders to it and it will show your images.
For speedy resize to web etc I used 'Export Picture to folder' in the file dropdown menu - I think it defaults to a 'Picasa Exports' folder with subfolders of the same name as the one you are exporting from and you can select the resize you want (I usually used 800pixels as that seems a good size for uploading to websites).
I no longer use this method as I use Lightroom 3 now, but its how I started while I was deciding what editing software to use.