1. you create the adsense custom island
2. for each forum you set the 'Guest' permission to 'Must view ad island' to 1... (actually to ANY other user group as well..) those that don't need to see the advert, are set to 0
3. specify the custom island you just created (best bet is to use a horizontal type advert) for the forum as well..
4. repeat #2,3 for each forum.. rinse / repeat
clear cache, just cuz...
Done
