The picture is just too small to be able to see what it might be.

Okay, I've got a link to my flickr page. There are a couple photos up there, but this one shows the seed pods that are ready to attack our yard some more. ;)

Here is a link that might be useful: http://www.flickr.com/photos/ritanadhazy/

Ailanthus altissima.

'Weed tree' plus 'stinky' almost HAS to be Ailanthus altissima, lol. Why something that smells like a well used fire hydrant or cat box would have the nickname Tree of Heaven is beyond me.

Ayup, Tree of Heaven. While small you can cut them off at the soil line, although they will grow back until you have cut them back often enough to deprive the roots of needed nutrients and the roots die. Yours has seeds so it must be much bigger and will need careful consideration on how to remove it, maybe by a professional. This tree is one that you do not want to compost the seeds of, they will spread everywhere.