The problem here is that CDs don't work like other types of media, they have a ISO 9660 or Joliet file system for cds and Universal Data Format (UDF) for DVDs. There is no such thing as NTFS, FAT, FAT32, ect for CDs and DVDs.
Writable CDs range in size from 650MB to 900MB in size, with 700MB being far more common than the others. Single Layer DVDs are 4.7GB, with dual layer being 8.5GB.
Typically when a cd is written to it is done in "sessions" when you burn a cd with most software if you plan on writing more data to it in the future you need to choose 'multisession' and do not 'finalize' but you will need to close the 'session'. If you don't close the session it won't be readable in other drives.
What Nero's InCD (and Roxio's DirectCD) does is allows the disk to be written to similar to a floppy, but these are ugly adaptations to the limitations of CD-R and DVDR disks.
How were you writing to the 650s? There is absolutely no difference in the process if have CD-Rs. If you have blank DVDs now, then you will not be able to write to them without a DVD burner.
What you will need to do if you want it to behave like a floppy is use InCD and make sure you close the session if you plan on reading the disk in a computer that doesn't use InCD (or at least thats how it works with DirectCD). These are really terrible solutions though and if you can just accept a different way of dealing with the media you will be better off and more compatable with other computers.