This article says it's in beta and not accepting applications at this time. https://www.google.com/adsense/support/bin/answer.py?hl=en&answer=20012
currently now feeds are not able to place adsense ads, hopefully they can and it will defintely increase our earnings
if you want this you can make changes in in rss files ...if it .php ....you can use echo" " to show your ads.
Check here: http://www.viniciusbalan.com/blog/2007/06/23/google-adsense-in-feeds/ is possible i think to apply to beta test.
RSS Feeds offer updates - all at one place, just like your morning newspaper. You can "subscribe" to your favorite sites, that support them, and read them at any time. If you want to read online, you've got Google Reader, Bloglines, etc. If you wish to read offline, use software like the paid FeedDemon or the FREE FeedReader. Hope this helps...
you use XSL(eXtensible stylesheet language) and add adsense code into XSL source, then add XSL into feeds