Re the market: make sure the file didn't get renamed with a .zip or something else extension. It should have a .apk extension; if it doesn't, change it and run it again. (You may need to download a better file manager such as AndExplorer or another from http://wiki.archosfans.com/index.php?title=List_of_Applications_tested_to_work#Archos_5A_file_managers
I don't know that it's been tested on the very latest firmware, but it should
work. This is not a major update from previous firmwares where it is confirmed to work.