Hello !
I guess you are talking about Plop's boot manager, not Grub's, aren't you? I answer to you under the assumption.
Generally speaking, after having lost Plop's boot loader, because it became overwritten in the MBR by Window's one, the fix is easy to do: reboot your host from Plop's boot CD, follow the usual procedure to install Plop on the MBR, restart once again from the HDD et voilĂ ! Plop's MBR loader is smart enough to find back its binary code and past settings from the first 32KB clusters on the HDD, where for historical reasons there is no regular data written here. At that point, you should have got back the Plop splash screen which you are familiar with.
As you said to have installed a new OS on the host (not sure to understand which one, kubuntu or W7), your partition settings in Plop's boot manager setup might have to be adapted to the new environment.
Hope this helps.