Yes, to a point. This sums it up pretty well: http://www.askdavetaylor.com/can_i_have_adsense_and_other_ads_on_my_site_simultaneously.html
You can put any other ad in pages with adsense on it, as long as the other ads do not look similar to adsense ads.
yah, that link is way outdated.. you can use any other ad-system, even contextual based (like Yahoo or pubCenter) with Adsense, as long as your visitors can not confuse those other ads with adsense (ie, they cant look the same).. HOWEVER Remember that the other company (Yahoo, MSN, etc) may not allow you to use them with Adsense - so you have to read their rules.
You can use any ad publisher you like but they are to look different from the adsense ad templated with different colours and design. Then you will be fine. its on google TOS