I mostly use BRU for its regular expression support -and sometimes trying to get a complex expression into that 7-char wide edit box can be a bit hampering (hard enough to get regexes right).
I can think of a couple of ways around this without introducing re-sizable sub-windows (this app looks to be an MFC dialog-box-as-app, yes?) which is actually pretty hard to get rightunless you want to bring along that whole swarm of re-sizable docking windows "stuff")
One way might be putting a set of tabbed windows in the the middle area (grey delimited box titled regec -- repl --remove -- add - etc).
Another might be to actually have two or three "layouts" (still with fixed sizes, so going from a fixed resource to a couple of fixed resources but not dynamic) and switch between them in a "view" menu item.
Thanks for even thinking about this!
Bob
PS: Don't get me wrong - I really like BRU, and particularly like being able to rename with regexes...