I can't say that I have seen any real "smoking gun" evidence to tie the two together, but common sense says the possibility is there.
This article highlights some of the possibilities and connections...
http://www.opinionjournal.com/extra/?id=110003213
I think we have to be careful that Nations such as Iraq don't advance their own agenda of killing Americans by providing WMD's to terrorists. After all, it is not the terrorists that we have to worry about creating WMD's.
There may be no smoking gun, but I would say the odds are in them collaborating against us.