Ansi.sys is in C:\Windows\Command
That said it is a long time since I ran anything but a simple program in Dos...... If you alter the config.sys file you will slow things up on booting for all your normal Win98 stuff.
Also there may be trouble when you have to choose between booting to the DOS command or running a DOS command from Windows...... So what, that's part of the fun with a computer....isn't it?