Originally Posted by vadkutya
if you deleted ubuntu you deleted grub as well. now there's no bootloader in the MBR which means you have to install on.
Not true, unless "deleting Ubuntu" means also somehow formatting/scrambling the MBR part of the disk. If the Ubuntu partitions are removed, and the Grub that is in use was installed with Ubuntu, it means some of it's files (such as configuration file menu.lst) are lost because they reside on the /boot partition (or root partition of Ubuntu, if no separate /boot was created). However Grub (or the pieces of it that are not on a normal partition) doesn't vanish from MBR; it just doesn't work, because parts of it were removed along with /boot.
To be able to boot several operating systems you need a bootloader, and it's probably best to put to MBR because that's the "dedicated place" for it. If you are using multiple operating systems, I recommend creating a dedicated /boot partition (big enough to hold all operating system kernels, if they put them there) where the bootloader-specific files are (and kernels). Then you can install as many operating systems as you like and remove/move them at will, as long as you just remember to configure the bootloader (Grub: menu.lst, LILO: lilo.conf) so that it "knows" where your current operating systems are (root partition, kernel, initrd, ...)
I thought Ubuntu had some "extra options" for the bootloader, but nevertheless the default option to install onto MBR is what you should use anyway, unless for some reason you don't want to erase Windows' bootloader (no reason for that, it can be recovered if you later want to use only it, and no other bootloaders). With multiple operating systems it's best to do some manual partitioning, and share common partitions such as /boot and/or /home - saves space and nerves.