How does the nikon d3100 compare to the canon T1i (500 d)?

I'm undecided and they both seem to have equivalent features…

Except the Nikon D3100 has Auto Focus in video, while the Canon doesn't.

http://www.dxomark.com/...nd2)/Canon

The D3100 has one feature that the canon does not- which is autofocus while shooting video.
If you are still undecided, I suggest you go to a camera store, hold each one and do some test shots (bring your own SD card so you can view them on your computer). See which one feels better in your hand, etc.

You can't go wrong with either

What you're being told above about auto focus is true. However consider this. I have a camera that does video with auto focus. In this camera, the Fuji 9000, the focus swings wildly causing blur for all kinds of reasons while people are moving about. Really you don't want it for that reason. Every time you move the camera for a shot or if people are moving around in your shot your focus will constantly change causing lots of needless blur.

I also say this because I own a t1i. I like the focus just the way it is.

D3100 has less noise, better quality and is lighter. It has better video with also auto focus while recording. It's also $50 cheaper if I remember.

Here's a post called 'Buying a DSLR, what's important, megapixels, features, brand, price, quality and which one to buy - http://www.the-dslr-photographer.com/2009/03/which-dslr-to-buy.html

Good luck! The site has many more tutorials, tips, reviews and guides!