Recently I tried to write a CD using my DVD writer (MSI DR8-A2 (±r ±rw)) and it hung at exactly 50%. This happened on mutliple occasions and has left me with a lot of coasters. (yes a CD with a DVD±R - I have no problems writing DVDs by the way, only CDs)
So to test if it was just the drive, I installed my old CD writer (artec 48x12x48x - cant remember other details :x).
This also kicked out the disks at exactly 50%.
I tried using different disks, which also hung at 50%.
Finally I have tried using both drives (separately) in another computer with a fresh install of nero 5.5. And only to get the same result.