The Mega 2560 should have enough memory if the standard Arduinos don't.
MarkT, afaik a running sketch cannot repleace itself unless it's the bootloader who does it but then again the bootloader might be to small to boot from the internet, maybe it could from the sd card wich would be fine for me, one could download the hex file to SD and then reboot.
erik
Perhaps I was not clear. I am not trying to interface to the Arduino via its ethernet port. I was trying to comunicate via the USB port and using the Inernet to get the data to the remote Arduino. The arduino would behave as it would with a cable connection if the USB adapters could make the transfer transparent.