Pop-up text boxes?

I'm assembling a presentation to help teach reading in a primary school. I'd like the teacher to be able to click on a word in the text which displays a pop-up box explaining what it means.

e.g. click on "Britain" and it displays a pop-up box saying "a country in Europe".

Ideally the text in the pop-up could be formatted with a different font, bold, italics etc.

I can't work out a way to do this in PPT that doesn't involve creating a separate slide for each definition ( nightmare!). Any ideas, anyone?

I'm using ppt2000 on Win XP.

Thanks.

While not the cleanest method, you can insert comments to do this. the only catch is you have to view the presentation in edit mode to see them and they appear as additional post it notes on the slide.