Is the cd in the Mac format? I doubt a standard x86 iso will boot. I think it is hpfs or something like that. BeOS used to make a disk that had dual formats on it somehow.

Some where during the lime time of Tiger as fare I remember Tiger 10.4 Apple released Bootcamp
Bootcamp while help youn to repartitioned you're hd and install windosz or GNU linux .
Before that there was BOOTCAMP beta.
Do you have BOOTCAMP

The way that I understand it, is that the Mac O/S cannot be completely erased from the hdd.

rather it is need to boot the box & then transfer control to the "other O/S".
that is, the Mac O/S hdd partition is reduced in size to the bare minimum to boot the machine,
and the rest of the hdd is given over to the "other O/S".

the amount of the Mac O/S also is needed to be reduced, by erasing all unnecessary files / programs,
to enable the reduction in size of the Mac O/S itself, & therefore its partition size.

Why isn't it possible to get rid of Mac OS?

It depends on how you're MAC is configured.
As a example MY MACintosh Hd only contains the OS X.
The data are on different other drives .
But the Macintosch HD is about 320 GB .
So if I wish to dual or triple boot than I shrink the Macintosh drive with no problems at all.
One of the options to do the job is to make use of Bootcamp
OSX does not take so much space

But the OP probably does have 'Tiger' on the hdd - so it may need to remain, in order to boot that old Mac...

& probably a smallish hdd, as well. so, as above - a remnant of the Mac O/S, could be needed to achieve a boot-able hdd for the "other O/S".

If, when you look at the CD you see one file called debian-504-powerpc-CD-1.iso then you burnt it incorrectly. You should see lots of ordinary files. You need to burn the disk as an iso image, there are instructions all over the web for how to do this. Search on burn iso image to cd
If you are doing this with Mac OS, then it will not let you, because you cannot partition a disk you are running from, only one that is not in use ("not mounted").

Once you have correctly burned and booted from the CD, the distro's installer should offer you a partitioner that will work.

A .iso file should NOT be just written to the CD as a file!

It's actually a raw "image" of the individual bytes on the disk that make up files. It sould be burned as an image, not as a data disc.

agree with MTK358, use something like Brasero or K3b to burn the ISO

More precisely, if you burn it as a file, all the data is still there, but it's all in a single file in a brand new file system written to the disk. If you burn it as an image, then you're preserving the file system data that's in the .iso itself.

Unless the OP has a Linux machine available, I think that's a no-go.

But seriously, there are good CD-burning programs out there for Windows that will burn ISO images to a CD properly. One of which that I used to use is ImgBurn, and it's freeware (not FOSS, but it's free as in gratis).

EDIT: Oops, I'm forgetting the OP is on a Mac. Dunno about image burning software for Mac, but I'm sure there's some out there...

A more precise way to put it:

If you burn it as a data disc, the disc is formatted with a filesystem, and then the iso file is added as a file in that filesystem.

If you burn it as an image, the file is burned directly to the disc, no filesystem. In fact, the ISO file itself actually contains a CD-ROM filesystem in it!

Another thing, it sounds to me like you have an older Mac that uses a PowerPC processor. If this is correct, then the format of the ISO file doesn't matter, you just have to download a distro for that matches your processor! For example, go to http://www.debian.org/CD/http-ftp/ and click on the 'powerpc' link to download a Mac compatible version of Debian. You can use it to erase Mac OS entirely (which is a one-way trip!) and just use Linux, along with ext2/3/4 file systems and everything Linux related

Errr, that's just what I said, wasn't it?

Nothing this thread hasn't said, but I'll try my own explanation:

1) You MUST boot to your OS10.3/Panther CDROM or Debian CDROM in order to erase everything; i.e. there is no way to boot up normally and do it.

2) If you know you want Debian (my vote!), just boot to that CDROM and follow along. You can easily do this by holding down the "c" key down while booting up (and having the disk in the drive) and at the "boot:" menu, just hit Enter.

Since you are having trouble, you could have a bad optical drive or more likely trouble as tredegar and MTK358 mentioned. Put the debian-504-powerpc-CD-1.iso file on your desktop, then open Terminal (look in Applications, then Utilities) and type "hdiutil burn Desktop/debian-504-powerpc-CD-1.iso", and you should have a working disk.