Rehan - 5:19 pm on Aug 5, 2008 (gmt 0) (variations = synonyms, etc.)
I've read in a few places that the only difference would be that the broad match would also catch "rivers" as well, but I've seen it suggested elsewhere that it would also match synonyms of the word; I.E. stream, creek, etc...
I'm pretty sure that negative broad match is not "expanded" like broad match keywords are. As it says at [adwords.google.com...] :
"It wouldn't prevent your ads from showing on variations of these terms, however."
(variations = synonyms, etc.)