http://bugs.winehq.org/show_bug.cgi?id=25155
--- Comment #3 from A Wine user RandomAccountName@mail.com 2010-11-13 16:59:45 CST --- If I understand correctly (and I wouldn't guarantee it) the difference after that commit is now the PROCESSOR_ARCHITECTURE environment variable is set to AMD64 instead of x86 for 64-bit prefixes. Changing the value to x86 in HKLM\System\CurrentControlSet\Control\Session Manager\Environment makes the installer work again.
According to this:
http://msdn.microsoft.com/en-us/library/aa384274%28VS.85%29.aspx
...this variable should be set to x86 on the 32-bit side of WoW64, while the real processor architecture is relocated to the variable PROCESSOR_ARCHITEW6432.