CD written in disk utility not readable in PC + rendered "un-re-writable".

I am trying in vain to burn more than one session on the SAME CD. I tried disk utility, because toast doesn't work. I created two disk images of my folders; "waves.dmg" and "karaoke.dmg". I chose "read/write" which - according to the manual - should make it possible to write more disk images to the CD at a later time. Problem #1: the CD doesn't work in my PC! My PC thinks that the CD is empty. Problem #2: I cannot write on the CD again! The CD is refused by disk utility, when I try to add (write) to it again. Is there a way to do this? It is driving me nuts! I just want to know if it is possible or impossible. Getting tired of trying. Is there something wrong w. my recorder?

iMac Mac OS X (10.4.5)