From the commandline, try this:
<code>
cd /where/your/files/are
tar cf - .|mkisofs -stream-media-size 358400|cdrecord dev=$DEV speed=4 -v -
</code>

The 358400 is for 700 MB, replace with 327680 for 640 MB. Before you run above command, run this:
<code>
cdrecord -scanbus
</code>

This will give you a list of "scsi"-devices and "addresses". You must replace the $DEV above with the address
associated with your burner, e.g. "1,0,0" (without the quotes).

This will not work with newer Knoppixes (>3.6?) if your burner is attached via usb.