You can minimize the "size twitch" by adjusting the size of the original window out to the dimensions returned by Get (ScreenWidth) and Get (ScreenHeight). Then, when you close the new window, include a script step that maximizes your windows to return the original window to it's maximized state.
I use this technique to open a "search palette" in my Known Bugs List database. If you are interested, download a copy and check out the scripts that open a search window or the one that opens an edit window for the version history. You'll see this technique implemented plus a few other ideas for properly managing such popup windows--including a custom menu that enables the close window control in the upper right corner of a window that appears to be "modal".
Thanks so much for the information. I have been a bit fustrated since our system is also accessed from the web. According to the documentation, new window is a viable script step using IWP; however, it is not working for me. I am using OS 10.5 and FM 11. We had to come up with a different approach.
That being said, I hope to use what I have learned from you in the future.
Thanks again. Carolyn