iTunes won't update - getting error

I'm trying to update iTunes from 10.0.1 to 10.1.1 on my Mac mini 1.83 Intel Core Duo running OSX 10.5.8 using software update. All of my other updates have worked consistently but iTunes 10.1.1 gives me an error message that says "The update iTunes can't be saved - a networking error has occurred. Cannot open file (-3001) Make sure you can connect to the internet and try again."

I'm sure I have internet and like I said my other updates have worked.