Low Disk space problem...HP noot book

[Pari]

Hi all,
My HP note book is arround 3 months old. It has Windows Vista O/S home premium.. Since a months back I keep getting warning Low diso space and I can see disk drive D:/ partition is ful.....which was setted for back up. I changed setting of back-up pointing to Drive E:/ that is CD drive. Now it asks me CD every time it backs up and I keep dening it.
I am afraid, was that right thing which I have done or was there any other better alternet I ould follow?
Please help me on this problem..

[mektek]

You have set your back  to write to a blank CD. that is why it is asking you to put a blank CD in the CD-Rewriter drive.