This is a repeated question, and I've already replied over there. The content is as follows:
If you already know how to use a boot floppy to make a bootable CD, and only don't know how to automatically switch to the CD-ROM drive letter after booting,
then you only need to solve the problem of finding the CD-ROM drive letter.
There are two methods:
1.Specify the CD-ROM drive letter: add /L:X to the end of the line with MSCDEX.EXE in AUTOEXEC.BAT on the boot floppy (X can be replaced with another letter). Note that CONFIG.SYS should contain this line: LASTDRIVE=Z
This method is simple and easy to use, recommended for beginners.
2.Use FINDCD.EXE to find the CD-ROM drive letter. This method is a bit more complicated; you can refer to the super moderator's MSDOS7.10 Super Boot Disk.
After deciding which method to use, add one more line at the end of AUTOEXEC.BAT on the boot floppy:
X: (the first method)
or
%CDROM%: (the second method)
Then after booting, you can enter the CD-ROM drive letter (of course, the drive letter of the first CD-ROM drive).
You can test it with a floppy disk first, and burn the CD after it works.
If you still don't know how to use a boot floppy to make a bootable CD, then first look through the old posts from before; after you learn that, do the above.