Hinduism is, of course, older than Christianity.
In Hinduism, it is not necessary to believe in a Higher Power to go to heaven (or attain Moksha, which means to be one with the Being). In Hinduism, to reach that, all you have to do is do good things and earn karma. This makes atheists and people of any religion and everyone in between eligible. However, in Christianity, to go to heaven, you must believe.
That's the one that leaps to mind...there are many more, but I'm not going to list them all here. Check out the workpieces of Hinduism and Christianity for more detail.
By the way, a common misconception about Hinduism is that it is a polytheistic religion. It's not. Not really, anyway. Hindus believe that there is one Higher Being that takes the form of many different things. God is in everything, including plants, animals and humans. (Therefore, in Hinduism, looking inside you to find God is okay. In Christianity, you must reach outside of yourself to find God.) But there is only one Higher Being.
Honestly, they have a lot of differences but a few (gasp!) similarities as well. However I'm tired after studying for midterms all day and now Imma log off. Hope I helped!