You can try gatesfoundation.org, and microsoft's giving page (215 million last year, apparently). Don't know about the more detailed reports, must be some USA goverment body that holds and releases this info, isn't that a requirement in US. After all most of it is for tax break and marketing reasons.
For some reason Opera does not want to connect to the microsoft site, not sure why - maybe my app. is scared it may catch something, ha ha ha.
I hate gatesie and what he does professionally, but donating may be genuine, maybe his wife is a really nice person.