Qt 4.7.1 now available under lgpl, choose between VS2008 or MingW compilers (for windows) available on all major platforms, also comes with great documentation

newer versions for softwares/libraries/compilers already mentioned here:
- wxWidgets (2.8.11)
- SDL (1.2.14)
- netbeans 6.9.1
- code::blocks 10.05
- MingW 4.5

any compilers that support or partially support the latest standard (C99 and C89) the list is here: http://en.wikipedia.org/wiki/C99#Implementations
on Linux system you probably already have gcc -just check the version to make sure it's the latest, if you're using windows then you can either build your gcc from source or get mingw to make your life easier or get an IDE plus compiler like Code::Blocks or Visual C++ Express

Can't answer that, never did the research. Try mingw-gcc or code::blocks if you're on windows

Generally the command line M$ compiler will use C rules when compiling *.c sources and C++ rules when dealing with *.cpp files, i.e you just invoke "cl c_source.c" or "cl cpp_source.cpp" in the MS Visual Studio Command Prompt™.

Try Vim (www.vim.org) as an alternative to Notepad/PFE/Edit.com, it works very well in teh command prompt. But IMO the best is that you actually learn to use the MSVC++ IDE.