iBook G3 - DMG files won't mount!

I recently acquired an iBook G3 Clamshell (366 mhz) with Tiger (10.4.11) installed on it.

I can't seem to download dmg files, as I get a 'Mounting Failed' error. I have tried creating a new admin, no luck. Unfortunately, the computer didn't come with the Tiger install cd's. I have also tried verifying and repairing the disk permissions with no luck.

Any help would be greatly appreciated. Thank you!