This post and all the links I've put in it will show you how and what you will need.
A little tip for all you novice forum members - Anything like this is easily found on the forum by the search button - see at the top of the page just under the lurid green Archos label! All you do is click on this then type "external microphone" into the search window and click on "search all terms" and in this case it points you straight at a few posts on the topic of interest....see all very easy/takes 5 seconds!!!
You can get VERY HIGH quality recordings with the method shown in this link with Gen 4's, the only limitation really will be the quality of the microphone you use and your skills in microphone placement!
http://forum.archosfans.com/viewtopic.p ... microphone