To be able to boot from the cd you may need to change the bios configuration. During the first moments of startup you'll probably see a message that says something like 'press <del> (or f1 or esc) to enter the bios menu'. Once you are in there look for a line about boot order and set it so that the cd is your first option (make c your second - if the cd fails you'll still boot into your system). Save and exit and try again.
About partitions, the sizes indicated are fine, but I'd suggest you also make another partition for /home where your personal files will be stored. That way if you totally mess up your system to the piont of needing to reinstall your data is safe.
Don't worry too much about creating the partitions or formatting them. If you are going to install any of the big distros (and I suppose kubuntu could be counted as one of them) you'll have access to an easy graphical partition / format tool during installation.
Finally, a live cd, apart from being useful to get an idea of what a distro is like without actually installing it on your system, is a great tool for system rescue operations (also for windows!!). Knoppix is probably the most famous one. I peronally also love SystemRescueCD
, which is small (virtually no gui) but packed full of rescue tools. Using one of these cds you can get access to your HD and either make the necessary changes to the configuration files to be able to get it working again, or salvage the information that is on the disks. I recently used it to get some crytical files off a neighbours pc with XP which had suffered a fatal virus attack.