It has to be substantially changed from what you printed on the web for the first rights to still be available.Consider it self-publishing when you put stuff on the web. There are publishers that may be interested in taking something that has been self-published, but the only cases I have heard of that actually worked involved material that had been self-published in small print runs in hard copy.
Self-publishing on the internet means that millions of people can read what you wrote. In that case, publishers figure that there's not a large enough market left for them to make any money by printing it in hard copy.
So it's not just that first rights are gone, but the market is used up, too.
[This message has been edited by Kathleen Dalton Woodbury (edited November 08, 2004).]