Ah, it works when you first use burn:/// to compile the cd and then start n-c-b from the command line (that cost me another dvd to find out :-( ). I get the following output:

launching command: growisofs -dvd-compat -graft-points -path-list /tmp/iso-wouter.BLFS7T -Z /dev/hdc -input-charset utf8 -r -J -V Personal Data, mrt 14, 2008 
growisofs stdout: Executing 'genisoimage -graft-points -path-list /tmp/iso-wouter.BLFS7T -input-charset utf8 -r -J -V Personal Data, mrt 14, 2008 | builtin_dd of=/dev/hdc obs=32k seek=0'
growisofs stderr: Using SPANI000.MP3;1 for  /spanishpod_E0084pr.mp3 (spanishpod_E0080pr.mp3)
growisofs stderr: Using SPANI001.MP3;1 for  /spanishpod_E0080pr.mp3 (spanishpod_E0074pr.mp3)
growisofs stderr: Using SPANI002.MP3;1 for  /spanishpod_E0074pr.mp3 (spanishpod_E0070pr.mp3)
growisofs stderr: Using SPANI003.MP3;1 for  /spanishpod_E0070pr.mp3 (spanishpod_E0064pr.mp3)
growisofs stderr: Using SPANI004.MP3;1 for  /spanishpod_E0064pr.mp3 (spanishpod_E0060pr.mp3)
growisofs stderr: Using SPANI005.MP3;1 for  /spanishpod_E0060pr.mp3 (spanishpod_D0085pr.mp3)
growisofs stderr: Using SPANI006.MP3;1 for  /spanishpod_D0085pr.mp3 (spanishpod_D0077pr.mp3)
growisofs stderr: Using SPANI007.MP3;1 for  /spanishpod_D0077pr.mp3 (spanishpod_D0075pr.mp3)
growisofs stderr: Using SPANI008.MP3;1 for  /spanishpod_D0075pr.mp3 (spanishpod_D0067pr.mp3)
growisofs stderr: Using SPANI009.MP3;1 for  /spanishpod_D0067pr.mp3 (spanishpod_D0065pr.mp3)
growisofs stderr: Using SPANI00A.MP3;1 for  /spanishpod_D0065pr.mp3 (spanishpod_D0057pr.mp3)
growisofs stderr: Using SPANI00B.MP3;1 for  /spanishpod_D0057pr.mp3 (spanishpod_D0053pr.mp3)
growisofs stderr: Using SPANI00C.MP3;1 for  /spanishpod_D0053pr.mp3 (spanishpod_D0048pr.mp3)
growisofs stderr: Using SPANI00D.MP3;1 for  /spanishpod_D0048pr.mp3 (spanishpod_D0042pr.mp3)
growisofs stderr: Using SPANI00E.MP3;1 for  /spanishpod_D0042pr.mp3 (spanishpod_D0038pr.mp3)
growisofs stderr: Using SPANI00F.MP3;1 for  /spanishpod_D0038pr.mp3 (spanishpod_C0083pr.mp3)
growisofs stderr: Using SPANI00G.MP3;1 for  /spanishpod_C0083pr.mp3 (spanishpod_C0078pr.mp3)
growisofs stderr: Using SPANI00H.MP3;1 for  /spanishpod_C0078pr.mp3 (spanishpod_C0073pr.mp3)
growisofs stderr: Using SPANI00I.MP3;1 for  /spanishpod_C0073pr.mp3 (spanishpod_C0068pr.mp3)
growisofs stderr: Using SPANI00J.MP3;1 for  /spanishpod_C0068pr.mp3 (spanishpod_C0063pr.mp3)
growisofs stderr: Using SPANI00K.MP3;1 for  /spanishpod_C0063pr.mp3 (spanishpod_C0058pr.mp3)
growisofs stderr: Using SPANI00L.MP3;1 for  /spanishpod_C0058pr.mp3 (spanishpod_C0055pr.mp3)
growisofs stderr: Using SPANI00M.MP3;1 for  /spanishpod_C0055pr.mp3 (spanishpod_C0050pr.mp3)
growisofs stderr: Using SPANI00N.MP3;1 for  /spanishpod_C0050pr.mp3 (spanishpod_C0045pr.mp3)
growisofs stderr: Using SPANI00O.MP3;1 for  /spanishpod_C0045pr.mp3 (spanishpod_C0043pr.mp3)
growisofs stderr: Using SPANI00P.MP3;1 for  /spanishpod_C0043pr.mp3 (spanishpod_C0040pr.mp3)
growisofs stderr: Using SPANI00Q.MP3;1 for  /spanishpod_C0040pr.mp3 (spanishpod_C0032pr.mp3)
growisofs stderr: Using SPANI00R.MP3;1 for  /spanishpod_C0032pr.mp3 (spanishpod_C0028pr.mp3)
growisofs stderr: Using SPANI00S.MP3;1 for  /spanishpod_C0028pr.mp3 (spanishpod_C0025pr.mp3)
growisofs stderr: Using SPANI00T.MP3;1 for  /spanishpod_C0025pr.mp3 (spanishpod_C0017pr.mp3)
growisofs stderr: /dev/hdc: "Current Write Speed" is 12.3x1352KBps.
growisofs stderr: :-[ WRITE@LBA=30h failed with SK=4h/ASC=08h/ACQ=03h]: Input/output error
growisofs stderr: :-( write failed: Input/output error
growisofs stderr: /dev/hdc: flushing cache
growisofs stderr: /dev/hdc: closing track
growisofs stderr: /dev/hdc: closing disc
process stdout: HUP
process stderr: HUP