I'm trying to install Windows 7 64bit (as oppose to 32bit), mainly because large amount of RAM would be wasted otherwise.
I wonder if I should install Visual Studio 2008 32bit OR 64bit. I also uses Qt 4.5/4.6 for development, does it play well in 64bit environment?
Any suggestions on what will be a most recommended configuration?
If 64-bit applications (which may need a lot of memory resources, e.g. Compilers, IDEs and rendering programs) are available, you should always use 64-bit, in order to fully utilize your memory and optimize the performance.
I don't think there are any 64-bit versions of Visual Studio available. This makes answering this question easy: choose 32-bit Visual Studio.
This doesn't prevent you from actually compiling 64-bit applications if you choose (i.e. need) to do so, however. You'll need to compile Qt yourself to generate the 64-bit libraries, but other than that things should be fairly straightforward.
Now, on the other hand, if you don't need to develop 64-bit Windows applications (you probably don't), you can just use the officially provided compiled 32-bit Qt libraries for VS2008 and save yourself multiple hours building Qt. I've experienced no difficulties myself using 32-bit Qt on 64-bit Windows with Visual Studio 2008.