Trying to add Kit fails

Hello,
I had a QtCreator that ran with MinGW (I dowloaded the installer that did this). In a bid to fix a bug which seemed to be dependent on the version of Qt I decided to upgrade to Qt 5.3.1.
I uninstalled my previous versions of Qt (because the installed told me I already had a c:\Qt folder and this was preventing me from installing Qt).
Then I dowloaded the "default version" of Qt. It turned out this was based on MSVC (which is installed on my PC, 2008 professional and some more recent Express versions).

So I installed that, it seemed to install, but I could not debug anything like I used to. I got that nasty "No debugger set up" message. I tried looking around on forums and got the idea
I had to look at a page on Microsoft's site to get the debugger. You mean to say that the Qt installer could not do this for me? Anyway looking at that site I was confused, do
I need to have a licence for a professional version of MSVC? Certainly I could not rely on my VC 2008 compiler because I'm trying to use C++2011 features.

Luckily I have another PC, on which I installed Qt 5.3.1 based on MingW. I can do some debugging there.
But I thought I could possibly add kits, after all I do have directories named c:\MingW and c:\MingW64. Somehow their presence does not seem to be detected.
I wondered if this is due to the registry being overzealously cleaned by the Qt uninstaller.
I had a try at installing a kit manually with Qt Creator's Tools > OptionAdd. I was just guessing here: I entered g++.exe in Compiler Path
and did not have a clue about what platform codegen flags I should add.
Anyway eventually I had MingW in the list of Autodetected Compilers inside Tools>Options>compilers.
But suppose I create a new project, then there is a Kit Selection dialog that appears. It doesnt propose a MingW compiler at all.
What's more, I'm supposing that MingW64 is a separate compiler. If I try to add that manually I get a message that it has already been installed, thankyou you very much, so please dont try this again. But it certainly does not appear in the list of available compilers, let alone in the compiler kits.

So you see my main goal is to be able to use the debugger. I dont care too much if the debugger is for MSV, but the documentation and environment is not really friendly, so I need a bit of help.

Update:
Having tried to install the Windows 7 developement SDK, it failed. The workarounds are too complex. I will uninstall Qt Creator made for MSVC and use the MingW version.