Try using windows 7 built in function to do this.
.. Go to control panel, select backup, then select create system backup.
.. This will create an image of the "c" drive to distination (HDD or DVDs). when completed it will prompt you to create a Bootable repair disk to restore the image.
The problem, I think, is related to the amount of data to be written to a given disk. The amount of space is greater than what can "really" be writed to the DVD disk even though it is less than the advertized size. I seem to remeber reading about this but can not find the source. (Added, this in not the base 10 vs base 2 diff where a 4.7 gig disk only holds about 4.3 gigs)