> Do the new dual-sided burners also burn the single-sided DVD's?
Yes. They all should. At least this is true for the the Sony DW-D22A, also known as the DRU-710A, also known as the LiteOn SOHW-1633S. For the past month or so I have found it to be quiet, fast, and reliable. I am burning with InterVideo DiscMaster 2---Sony recommends a specific version of Nero when burning dual layer, which I have not yet tried. No drivers are needed with XP SP2 home or pro.
The DW-D22A is the OEM version of the drive, i.e. no bundled software or cables. Purchased through
http://www.newegg.com for about $65. Hard to beat, considering you already have the cables installed in your system and probably already have software with which you are comfortable.
The latest Pioneer drive (A08 or the new A09) is considered to be somewhat higher quality, depending on whom you talk to, but it is also more expensive at around $100.
After much research in December, I had it narrowed down to these two drives and chose the Sony solely because I was happy with my old Sony DRU700. I think either drive would work for you.
> difference in the longevity of the faster (8x) media
Can't help you with this one, as I have a spindle-full of blank Ritek 4x media that I bought in an optimistic moment and have not made my way through yet. But you can probably find the answer here:
http://www.videohelp.com
As for archival quality, I would avoid dual layers for now, and would also avoid the faster media. DVD+R and -R are fairly well tested formats, but the 8x media is too new to have much exposure and I doubt it would save you much time in the long run. Generally, the faster the media, the more delicate and finicky it is, and burning coasters can be very time consuming.
That being said---for archiving 160GB you can hardly do worse than going out and purchasing a 200GB hard drive. For less than $150 you will have a live backup that is of far more reliable quality than any optical medium. Continue the offsite storage practice, but for an immediate backup, adding a new drive is a great way to ensure reliability in the short (and long) term. In fact, I just checked and Newegg has a special on the Maxtor DiamondMax 200GB drive for $104.89. At that price I may buy another one myself!
Heck, even if you buy a drive, write your data to it, and then pull it out and store it offsite (in the static-free bag it came in, of course), it should still be readable a year later by any computer than has an IDE/ATA interface (i.e. all windows machines for the foreseeable future). If you pull it out of the safety deposit box and rewrite it annually I think you will have the most reliable backup possible for the price.
Hope this helps!