<p>the company I work for want to use a "hosted payment form" to charge our customers. A question came up on how we can populate the "payment form" automatically with information from one of our other system. We have no control over the hosed payment form, and we have to use IE. Is this possible at all? And if so, how can this be done? </p>

<p>If something is unclear, please let me know...</p>

Unless your payment gateway allows you to pass through data in a set API (which lots do!), you'd need to take control (and responsibility) for your payment form.
I say responsibility because you would have to prove to your merchant account provider that everything is secure. This will probably incur some security testing fees too.
So check with your merchant gateway first. Lots of systems have the means to accept data from your site and their tech support will be able to give you a straight answer immediately. Otherwise you'd have to switch it over so you process all the data yourself which, just for making things easier, isn't worth it IMO.