Tricksy Cd Rom Burning

I recently hand-installed a cdr rw drive in my desktop along with Nero 6. I've having consistency problems in burning the CDs. Sometimes the burn finishes, but the write confirmation fails- then I discover that some of the files (most of them on one end of the directory) don't get written properly/at all, though the names are listed in the directory. I have experimented with reducing the amount written on the CDs (which are 80min 700MB Sony), and this seems to help- but I'm only reliably getting 500MB per cd. Is this normal?

It also *seemed* to me that when I went to "cd at once" instead of "track at once" I had more reliable results. Would this make sense?

Thanks for any advice!

"Steven"