It's hard to find out which platforms are supported.
There's this page in the documentation that lists the tested configurations: http://doc-snapshot.qt-project.org/5.0/platform-details.html
It doesn't say anything about MSVC 2008 (which is supported) or MSVC 2005 (which is not supported). Only the tested MSVC 2010 is mentioned.
There's this wiki page that lists the supported platforms:
Also, in Qt 4 we had this useful page in the docs:
Please bring back a list of supported platforms to the documentation.