A lot of people have trouble with k3b.I dont run kde or use that app but you could search "k3b" on this site to see how to configure it.OR you could just use the command line and be done.I am assuming you have both a cdrom and a cdburner.

Move some files you want to save into a folder named burn_cd (for example)
Make this folder into an iso :
#mkisofs -o my.iso -R burn_cd

Say cdrecord --scanbus and get the dev id for your burner (mine is 0,0,0)
0,0,0 0) 'CDWRITER' 'IDE4816 ' '482S' Removable CD-ROM

Burn your cd :
#cdrecord dev=0,0,0 speed=12 my.iso