Hi there mate,
Yep...I have a triple boot. One Windows and two Linux on a 500GB drive.
Nevertheless it is all more or less the same. I'll teach you how although I do not know what you have installed on your system at the moment [Win 7 + 8?].
You need to make sure that Windows 7 is installed first [on a single partition], then Windows 8 [again on another partition] then Ubuntu last. Ubuntu needs to be installed on a separate partition.
I will break this down a bit: The reason you install Windows 7 first and then Windows 8 is due to the Windows Bootloader. Windows 7 cannot
start Windows 8 so therefore you must install the newest Windows OS LAST
If you have a recent computer with the new UEFI technology [do some research on Google] you want to disable this BEFORE
any instalation and just use the normal BIOS. However, if you already have your Windows OS's installed then leave this the same way you had for the installation of Ubuntu [get the 13.04 version which is the latest and is very cool]
In regards to the Ubuntu install, you want to make a sole partition for that and leave it UNALLOCATED
. You will format that same partition as you go on the installation but you have to choose "Something Else" in the install option. Do not choose the automatic installation alongside with Windows!
Then depending on the space you have available for the Ubuntu partition goes like this [example only]:
When you run the Ubuntu disk and are doing the process of installing it you will come to a window to do the partitioning. To start click on the "+" and then you will see "free space" and then I think there is a button "Create"
Size: 300MB [do give this amount]
File System: ext2
Mount Point: /boot
/ [root Partition] Where all your system and future program files going to install
Size: [anything above 15GB. I gave mine 40GB on a 500GB HDD with 3 OS!!!]
File System: ext4
Mount Point: /
Size: [something like 50/75GB. I gave mine 100GB] This is where you can save music, docs, movies, videos...
File System: ext4
Mount Point: /home
Size: 1GB [people still don't agree on this one but even if you have only 2GB of RAM this 1GB will rarely get used. However if you only have 1GB of RAM give it 2 or 3GB]
File System: swap
The last thing is to fix the Bootloader or you will not even see Ubuntu...only the two Windows. You can fix this with a Linux tool called Boot Repair Disk Make sure to choose the Advanced Options and also to use Ubuntu 13.04 as your default Bootloader. Here is the link for the Bootloader fix: boot-repair-disk - Browse Files at SourceForge.net
Well mate I'm pretty sure that was of some help but if you still have any questions fire away.
Stay cool mate.