http://bugs.winehq.org/show_bug.cgi?id=9261
--- Comment #21 from Christoffer A christoffer.alf@gmail.com 2010-05-10 13:58:56 --- (In reply to comment #20)
http://www.eidosinteractive.co.uk/support/search.html?gmid=52 has 1.2 patches which may be what's required?
That patch does fix some issues with more modern graphics cards, but I cannot confirm if it fixes the issue with bad transparency.