On the note of making it look "more professional" (keeping in mind I have absolutely zero programming knowledge so this may be far more work than it would ever be worth) perhaps add a status bar at the bottom of the screen. Something to tell you what system/emulator you have selected, what version of ROMbrary you're running, what ROM you've selected, etc....Just anything that you may want a quick reference to using the program.
Also, adding cascading menus at the top - File Edit View Tools - would add a level of professionalism and familiarity I think. I don't know what you'd fit into those menus as it's a pretty simple program...Just a bit of input, hope it helps at all, and thanks for the awesome program!