I have an iBook with a CD-RW drive (it says...)

I have burned some pics but have in no way filled the disc...

Now, when I try to add some more from my burn folder (this is the first time I have tried this, despite having had my iBook for 6 months) it tells me to insert a blank disc.

Getting more info for the CD-RW disc, it does not seem to have read and write enabled but there seems to be no way to switch that on.

Does this mean I should have formatted the disc somehow, or that if I ever burn anything onto a RW disc, there is no chance to add or change anything?

I do have Toast 6, do I need to use that?

I have become so used to my mac doing everything for me - first time, logically, without any fuss or need for other programmes - that this has me a little stumped...

Obviously I COULD use a new disc but I want a bunch of pics on one disc to have them printed and logically, I should be able to re-write a re-write disc...

Ideas??