It shouldn't matter- except for the time factor-
it would take a lot longer to upload photos , because dial up has slower connection speeds. Did you try them 1 at a time?

for the avatar it does have to be the right size before uploading -
Avatar info - {Note: The maximum size of your custom image is 85 by 85 pixels or 64.0 KB (whichever is smaller).

If you need more help with your avatar there is a good thread in our Computer Forum-
http://neurotalk.psychcentral.com/forum36.html