I want to create a light-weight portable application in C/C++ for Windows. I don't want to statically link everything because I want to keep the size of exe as small as possible. I also use Dependency Walker to track the DLL dependencies of my exe file.
My question is that what are the list of DLL dependencies that an application can have and stay portable across different versions of Windows? With this list at hand I can check the output from Dependency Walker with the list and choose which libraries to link statically and which to link dynamically. I prefer the list contain OSes from Windows XP higher, but having Windows 98 in mind is also interesting.
Create a basic Win32 application in something like Visual Studio and check the dependencies with Dependency Walker. Those are your base dependencies. All of the standard Win32 DLL files will be required, including user32.dll, kernel32.dll, and so on. (Although some of this varies, depending on what you want the application to do. In some cases, you can get away with only kernel32.dll, but you won't be able to show a window on the screen. Probably a fairly useless app.)
Keep in mind that the last version of Visual Studio that can compile applications that run on Windows 98 is Visual Studio 2005. Visual Studio 2008 can target a minimum of Windows 2000, while VS 2010 can target a minimum of Windows XP SP2. You'll need to either use an older version of the compiler, or edit the executable file's PE header manually to change the subsystem field.
If you're really into things like this (although it's honestly a waste of time) you should investigate Matt Pietrek's LIBCTINY, originally from an article published in MSDN Magazine back in January of 2001. This little library makes it theoretically possible to use the /NODEFAULTLIB compiler flag in order to avoid linking to the CRT.