Thanks for all your help people!
just one more thing: Now I'm having some difficulties on handling my 20mb ibm5160 HDD contents using softwares such as PowerISO and/or Winimage. PowerISO works fine with my AT486 30mb image file, so I can insert and remove large amounts of files and after saving the .img file and converting it back to chd using chdman, it works perfectly with the AT486 driver. However, when I try to do the same thing with my little ibm5160 20mb HDD, it gets corrupted and the resulting .chd file becomes useless!! And Winimage seem to work with floppy disks only (and it is somewhat moody).
Which program do you guys use to insert files/folders or to remove them from a harddisk image (img or ima file formats) before converting it back to .chd using chdman?