Please consider using one partition for a separate home partition. This
makes it easy to install and re-install without disturbing your data and
settings. You will be much better served and will be glad you did. I can
step you through it. It isn't hard. However, you may need to either
re-install or move your home to another partition which is not as easy.

If you are using grub and not grub2 then it is just a text file that can be
edited and you can change or alter it to anything that you want. You can set
the default OS to another one. You can edit grub from any OS that you can
boot. You cna also edit grub temporarily on the fly by pressing e on the
line of grub that you want to change. When done making changes just press b
for boot and enter. If you are using grub2 that is another story.

Different flavours of Ubuntu can be installed to the same partition from
Synaptic and then you just need to change the session. Server can be removed
safely and depending on what is listed in grub you can still boot. Even if
it does work you can boot any live CD and rewrite grub. Everything is still
there you just need to rewrite the bootloader.