I"m not familar w/Nero, but I'd imagine it's similar to EZ CD Creator in it's operation. In EZ CD, first you open up the program and format a blank CDR/CDRW. Then you burn whatever onto it. Then (this is the step i think you are omitting) you go back into the program to close the CD. It gives you two options:
1. Leave CD as-is so you can write to it in the future
2. Make the CD readable in any CD Rom drive.
If you are going to try to read that CD on any computer other than yours, you need to make it readable. There is an option in there somewhere...there has to be.
You'll notice that if you have say, 100mb on a CD, there should be about 500 or so MB's left, right? Right. But if you "close" the CD to make it readable in any CDrom, that file mangler will show the CD as "full" i.e. 100mb/100mb instead of 100mb/600mb. Good luck.