@OP, dude, there is no way u can get use the rest space on the DVD.
But, if the DVD was not finalized while burning, there might be a slight chance of getting back the rest space.
Just try putting the DVD in writer and use any burning s/w. If the s/w doesn't detect it as "full" u may (remember "MAY")write additional data.
And others, why do u need win98 to read/recover lost session data? haven't u heard about "ISO Buster" type softwares...