(2)What should i set my booktype to if i want to write a dvd data disk
cos am finding all this concept of +R,-R ... a bit confusing?
You need to set the book type to dvd-rom for dvd+r media. Use Nero CD-DVD Speed, dvdinfo etc & if your 1640 came with software there'll be something there as well.
Once it's permanently set then you need do nothing further.
What you've now done is for every DVD you create , we're really talking movies, it will appear to standalone DVD players as a DVD-ROM (ie a pressed DVD) & gives a high level of compatibility.
As harley says low disk space is a severe problem. Not only for the reasons he's quoted but also it can severely affect your system performance as the operating system has to hunt around for space, which will be fragmented over the disk, whenever it needs to write anything to the HD.
If you use , say , Nero & create a data DVD you don't need the extra space as you just drag n drop directories onto the DVD. You don't need to copy the files into a special area. I'm guessing that no extra space is required for this.