No, it is NOT possible to create an operating system with Visual Basic (any version), because they require certain runtime libraries. Pre .NET versions require a file called vbrunxxx.dll (where 'xxx' is the version, such as '300' would be version 3.0) VB for DOS (version 1.0) requires a VBRUN100.LIB in order to run. This is true, even if you create a "self-contained" EXE file. All of these libraries require you to have MS-DOS or MS Windows installed, because they all are linked to Microsoft's OS-specific code (interrupts, external DLL's, etc), and cannot run unless you have those libraries. And those libraries require OTHER libraries, which require OTHER libraries (such as gdi32.dll and kernel32.dll - hence, an OS).
As for QBasic, it is technically not possible to create an OS because it requires runtime modules (these modules are linked into the EXE if you create a stand-alone EXE file), and they also use MS-DOS interrupts, which would need to be programmed from your OS EXACTLY the way DOS does (in essence, re-creating MS DOS).
Although it is *TECHNICALLY* impossible, it is not impossible on a theoretical level. If you had the patience and knowledge, you could create your own compiler for QBasic so that it produces pure code (not interpreted like QB code). This would essentially be creating a similar compiler as to Linux's gcc or Borland's DOS compiler for C/C++. Then, you could require that the QB program (the BAS file, not the actual EXE) declare "include" statements to add runtime libraries for functions such as file I/O and screen printing (this is what C/C++ does).
What it all boils down to is this: It doesn't matter WHICH language you use to create your OS... as long as there is a compiler that will create code that does not require libraries to run. The outcome of this language would be a VERY small key word base (if you look up the keywords for the core C language [not including those functions provided by #include lines], then you'll find that there are only a handful of keywords).
So the ultimate answer to this question is... No, it's not possible to write an OS in VB 6 because the VB6 runtime libraries are copyrighted by Microsoft, and therefore, you cannot create the proper runtime librarires in order to create your own compiler in order to write an OS with it. Also, regardless of which language you use to write the operating system, you MUST use ASM to write your boot loader, as it requires some pretty low-level stuff to make the machine useable.
I hope this helps. If you are still interested in using a BASIC style language to create an OS, then I would suggest looking into either creating your own BASIC compiler (prefereably a 32-bit compiler), or finding a copy of BASM (a BASIC to ASM translator).
