I learned programming on MS-DOS with DJGPP, which is basically the GNU Compiler Collection (and lots of other GNU software) for MS-DOS. It certainly was usable (and included two free IDEs: RHIDE and Emacs), it was as good as GCC on Unix except for the lack of multitasking (which is what led me to Linux). This was long before Windows 98; the earliest DJGPP I can find is from 1994, and I had already migrated from DJGPP to GCC on Linux before 1998.