More than just re-arranging the icons is needed, at least one of the icons is completely missing from the toolbar you provided: The "crayons" icon which is used to choose mIRC's text and background colors. There may be more differences, but that difference was (almost) immediately apparent.
I think a newer bitmap is needed. The one you supplied is dated August 22nd, 2000. I'm sure a few features have been added to the toolbar in seven years!
Please note, I'm not complaining, just clarifying things. I truly do appreciate your help!