Amercian Tax %

Hello and thanks for reading,

I'm currently creating a website which has potential to make large sums of money each month using YPN (Yahoo ads). Since me and my partner who will be running the site are not american and live in Europe we can not apply for Yahoo.

We have an american contact who will allow us to use their yahoo ads account and who will transfer the payment each month. Since the ads would be in our american partners name, they will be the one having to pay the tax. We will make sure we give our partner money to cover tax's and money for their time managing our ads, however as i'm unexperienced with US tax, is their a cetain tax % to take into account?

Regards,
Dan