Is it possible to convert a bootable CD ISO image into a bootable DVD?
The ISO image in this case is Ubuntu 10.04.2 desktop...
No action should need be taken. All ISO writing software I have encountered can successfully write a .ISO file intended for CD to DVD, such that the result may be used on devices expecting DVD media, assuming the underlying data is compatible.
My experience is limited to images providing bootable operating systems and media (movies, music) however, so it may be that this will not always be successful: in the limited case of the ISO files distributed by Ubuntu, it should always be true.