Loosing quality after CS5 and slideshow
I've only just spotted this post (I checked your posts to see if you'd posted any Lake Garda pics yet).
There should be no automatic change in resolution except maybe by the software used to create the slideshow or automatic adaptation to the screen resolution being used. My pics jpgs for web and slideshow are all saved at 72ppi (basic screen resolution). It looks just as good on my 50" TV screen (I use a USB flash).
When all else fails - read the instructions.