Hi John,
I'm not sure if this is possible. There was a thread recently about printing automatically, with a number of copies, and from my research then it seemed you can't bypass the printer dialog. If you do find anything though please let us know.
Remember it's the browser which pops up the dialog, not the page itself.
If it's an internal app then one option is to compile a custom browser, based say on the FireFox code, but that sounds like an extreme approach to me.
Cheers
Bruce