K3B does indeed write to DVD's, By default it may not appear as an option when you first start K3B, so in this case heres what you do,
1: start K3B
2: at the main start screen where you see your burning options click "burn DVD iso image"
if that option isn't there right click the main option area in a blank section and select add button, from the menu that appears select "burn DVD iso image"
The rest is just a case of selecting the iso you want to burn!
Hope this helps, let me know either way!