is there any software or any way to backup movies on dvd9 to dvd5 with win98.

I guess you probably could, but you would not be able to use the full DVD space on one title, because if the M2V and AC3, etc. added upto 4gig or more then you would not be able to remux... You could definatly not have a M2V greater than 4gigs.

If you ripped the DVD splitting the M2V/VOB so as to not breach the file size limit, then you could run the parts through DVD2AVI and re-encode at a lower bitrate using TMPGEnc, CCE, etc.

I wouldn't recommend it though, better just to upgrade to win2k or XP.