Posted 15 December 2008 - 07:57 PM
You'll want to create a split archive that spans volumes. Easy enough. I can't visualize the actual steps to take at the moment, but the built-in help should be enlightening. Search for "volume" and "span". That should get you some good results. I believe you can tell winrar how large each volume should be (it may have a preset for DVD, but I don't remember for sure.)
As for minimizing the total size, the best thing I can think of would be to set the compression level at Max. Bear in mind that with 70 gigs to process, winrar is going to take some time... a lot of time. Perhaps hours. If at all possible, I'd look through my files for any that I don't actually want.