Okay, I see.
It's resizing it probably because your source window is either maximized, or too large for both windows to appear in the same monitor. Unfortunately, there is no way, in classic mode, to prevent the Find Reseults window from "docking" itself to the edge of the source window (and resizing the source window, if necessary).
However, from what you wrote in your original posting, I get the impression that you have no great need for this window, and you would just as well not have it appear at all. If that's the case, you could just check off the "Show All Matches" option in the Find dialog, and this window will not come up. Would that solve your problem?
- luis