where will the program be ?
- on the CLIENT machine - then you'll have to make him download your app - and then it's not a problem to launch it in such a window (provided you coded it to execute in a pop up !!)
- on the SERVER machine - then i hope for you there won't be many peole connecting at the same time running the same app !!!!!!!! this shouldn't be hard, as it's only displaying the results of your app in a popup ...
(personnaly, if i had to release an euro convertor, i would either write a very light c++ or basic or whatever app, and make it downloadable to clients; or do it in javascript (or pure java) and run it client side - i mean, it doesn't require heavy processing ...)
viel geluck !!!!!