Re: DVD Disk quality
Never trust any single medium absolutely - really. This has been the case since the mighty reel-to-reel IBM 3420s, which only munched tapes you did not want munched.
If you venture into a geek forum you'll get some tips on the best brands - Verbatim and Imation come to mind - but no-one can safeguard your data apart from you.
For 115GBP you can buy an 320GB external HDD drive for extra peace of mind. Again, not to be trusted by itself, but faster and more convenient for a second copy. If it's really important, burn two copies onto different DVD brands, send one offsite somewhere and ask it to be checked when it arrives, and put a copy on the HDD.
BOFH