Is this the first presentation you've ever done, or something? O_o
Maybe I've just been very lucky, but I've been doing presentations since high school. I still hate them >_>
I don't think I have any of my old presentations still around, so I can't tell you a decent amount of words to put in. But it's really not about the number of words - you might be able to do a very good presentation with few words, or it might need a lot.
Best thing to do is to write down your speech, and then talk throught it. DONT rush the talk at all - in fact try and speak more slowly than usual. Once you know how long your speech takes, you'll know whether to cut it down or fill it up some more.