Cannot burn DVD under Linux?

[OErjan]

what is your burner? internal IDE, SCSI?
external like; usb, firewire, pcmcia, SCSI?
what is the devise named? the comands below will help with that

dmesg|grep CD

or

cdrecord .-scanbus

or

cdrecord --scanbus dev=ATAPI

dmesg|grep CD&&dmesg|grep DVD

if you try in the console we might get a "better" erormessage

growisofs -dvd-compat -Z /dev/whatever=/search/path/to/file.iso

replace the "/search/path/to/file.iso" with your searchpat (something like /home/knoppix/file.ISO)
and "whatever" is what one of the codes above give you, something like /dev/hdc, /dev/sda, /dev/ubb, /dev/scd0, /dev/rcd0c, ATAPI:2,0,0 ... should be among the output.