Use WineBottler to make a bundle for it (advanced tab) and check these boxes in the Winetricks section:
corefonts
flash
gecko
msls31
msxml3
riched20
riched30
tahoma
Then the textboxes should work.
More info: Wine Reviews : MSN Messenger 7.5 on Linux with Wine Wine Bottling On A Mac - #6 by spatiorift