you don't want to overburn your disks. In Toast, find the ISO 9660 file format (in the "other" section). This format has lower overhead than HFS/PC hybrid and lets you get the most data on a disc without sacrificing error-protection (which is what overburning does). That said, I've only seen as much as 702.9 MB available, but shop around; some media is larger than others. If it's a movie file you're trying to burn, consider cutting a few seconds off the end