This error is making me mad....it's happening more often than not now....feature length home vids can't be burned....mac ox x 10.4.8 ppc g4 dual core.....help!!! If toast won't work, what other mac osx apps can anyone recommend?

It's very odd that you have this problem at all. Toast has buffer underrun prevention turned on for -R or -RW media by default and the +R or +RW media have this built in. Personally, I haven't encountered a buffer underrun error since using Toast 5 in OS 9.

So something is very wrong here. What drive and brand of media are you using? Have you tried Save as Disc Image from the File menu and then burning the disc image using the Image File setting in the Copy window?