Yea, I'm lost too. What's PPM? Is it pay per 1,000 impressions? For Impressions, I use Adbrite, only because I lost my google adsense account but adsense is the best for impression conversions. Adbrite can be used alongside adsense. You can check them out here: http://adbrite.com
http://en.wikipedia.org/wiki/Cost_per_mille PPM - Pay per Mille - it is just a variaton of CPM - both of them means cost per 1000 impressions ( Mille in latin means Thousand - here's the proof from Wikipedia) also if You're looking fod CPM/PPM networks check out this list of CPM networks .
PPM = CPM. Pay per mille and cost per mille, respectively. Anyway, I think that the cpm program you're looking for is ADSDAQ. It offers a lot of flexibility because you can set your own rates as well as provide backup tags for unsold impressions. Here's a more detailed ADSDAQ review.