Yep, these things are pretty good as photo viewers.
The 404's screen is 3.5'' TFT (320X240 pixels) 4/3, over 16 million colors
http://www.archos.com/products/video/ar ... al&lang=en
Unless you plan to view these on a TV, you can resize all you photos very easily to 320x240, or a bit higher if you like to zoom in on them. I have Picasa too, and I love it.
What I suggest you try is connect your 404 to your computer and set it to PC Hard Drive mode, and in Picasa select/highlight a group of photos as many as you like, and click on the Export button. Set your 404\photos\ as the output directory, and select the resize option to whatever you want.
Once its done, disconnect it safely, and you should be done.