[gh0sth@cker]

The version of Nero that you have may be modified to only work with the same type of burner that it came with - so it'll only allow your burner to use it.
As for the buffer underrun - as the writer and old it may not have Burn-proof or Just-Link or any other technology similar to it.
When a cd is being written, the computer must supply a constant stream of data to the cd-writer or the burn will fail. A buffer of data is often used when burning a cd, this is to make sure there is data available to the cd-writer if the cpu suddenly stops sending the data for whatever reason. When this buffer runs out, a buffer underrun will occur as there is no data left to supply to the cd-writer. With burn-proof technology, when the buffer runs out, the cd-writer is still able to pick up from where it stopped burning.
As it may not have burn-proof, your friend will need to keep the buffer levels high. He can do this by not using any other programs while burning a cd, in other words don't put any more strain on the CPU when making a cd. A defragement of his disk may also help as the hard disk will be able to retrieve the data faster.