If you want to keep the Kubuntu install, and have the option to boot into it, but have the option as hidden as possible, you want to use 'hiddenmenu' in grub:
Open your /boot/grub/menu.lst file. (you'll need root privilidges so sudo [favourite text editor] /boot/grub/menu.lst will work)
Scroll to the line
(it's on line 23 of mine, which is probably where it is on yours) and remove the # from the beginning.
Then edit the number after the word 'timeout' a few lines up above to however long you want in seconds.
You'll probably end up with something like this:
## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
# Hides the menu by default (press ESC to see the menu)
What this does is make it so that on boot you get an option to hit <esc> to open the grub menu for however long you've set the timeout value to. Setting timeout to 1s is about as close to completely transparent as you'll get. Setting it to zero is the equvalent of infinity.
For my example, you get 4 seconds to hit escape before booting the default OS.