If you want packet writing, use DVD-RAM. It's the only format that does it properly, and it's very stable and high quality. CD-Rs and DVDRs weren't made for packet writing, it was an extra "feature" tacked on afterwards, that nobody has ever gotten to work correctly.
I find that CDR's are better at packet writing with DirectCD, Win XP, Nero's InCD, NTI's FileCD, and B's Clip.
A CD-R disk can hold approximately 700 megabytes of data. However, I recommend you don't fill it with more than 650 megabytes, because it needs some space to close the disk and this is where I believe most people have a problem with "Packet writing" since the software doesn't inform a user when its time to close the CDR disc! So, close the disk when it gets to roughly 650 megabytes full.
You can close the disk at anytime, however. It does not have to be full to be closed.