I have been messing around a bit more with editing disk images and my IsoCobbler application. Here is a newer version (and source in Visual Studio 2010) now with some extra features.
There are commands like NEW, which allows you to start from scratch with a blank FAT formatted floppy image (the 1.44 or 2.88Mb variety). You can also LOAD and then EXPAND your existing 1.44Mb images and IsoCobbler will attempt to make them into 2.88Mb ones, trying to keep the boot sector working in the process.
After writing the EXPAND command, which needs to transplant the boot sector and hack it around a little bit, I decided to implement an MBR command as well. This allows you to put in your own boot sector, or save the existing boot sector from a floppy disk image. Anyway, for details of all the commands, see the "Help" file included in the downloads. This version still expects all the files to be in the root, it doesn't support folders yet (which might be next on my list actually).
So after all that messing about, I have gotten as far as building my own boot sector in x86 assembler (using NASM, The Netwide Assembler) which in turn boots into my own simple kernel (and when I say kernel, I mean Hello World application). IsoCobbler did of course make a bootable ISO out of that experiment, so I have a bootable CD that runs my own bootloader and then starts my Hello World code as the kernel. Umm, now I'm feeling the need to go off and write a 'proper' kernel (in C probably). It seems that making a program to help me build CD-ROM images has gotten all out of control, since I seem to be considering the idea of building my own OS as a consequence. Right, I'm off to visit Bran's Kernel Development Tutorial, I may be quite some time...
What with all this fiddling around with boot disks and ISO files, I found that there were not many tools around to do *exactly* what I wanted ... namely edit a 2.88Mb bootable floppy image and turn that into a bootable ISO. So I've written IsoCobbler. It doesn't have a GUI, it is command driven, but it suits my purposes. Even though it looks very retro, this is a C# application running on .Net 4. Here is a screenshot of it in action, on Windows 7:
It comes with a default boot image included, and makes it simple for anybody to edit it. You can insert your own zip file called "content.zip" containing a batch file called "start.bat" along with any DOS applications you want. Anything inside "content.zip" will be extracted into a RAM Disk and "start.bat" will be executed when the boot disk runs.
I guess that it might also be useful for creating some sort of emergency boot disk, you could load the zip file with all kinds of tools.
So here is the application (you'll need .Net framework v4 installed and it's best to run it as an administrator) and the source code (Visual Studio 2010). Please drop me a line if you find it useful. If I get time I may fiddle with it some more...