The main site is http://atmelwlandriver.sourceforge.net/news.html. But http://www.wireless.org.au/~jhecker/atmeldrv/atmeldrv.html is also very useful.
To check if you have ATMEL device check table at one of the above sites or see instructions here(bottom). WARNING! Check tables at both above sites - I noticed that one of them was more up to date. You may also check the list of devices flagged as ATMEL in linux-wlan driver (which does not support them).
Joerg Albert suggested using another driver for AT76C503A avalaible at http://at76c503a.berlios.de