I don't know where a tutorial is, but to know what to do it would really help to know what you want to do.
I haven't recently installed a Mac OS, so I don't know whether the Mac installation process lets you use different directories for /, /User, /usr, etc. If it does, you might be fine leaving your Ubuntu partition where it is and creating different partitions for user data, applications, etc. This is however quite complicated and you may not want to get into that.
If you want to have Mac OS and Ubuntu permanently dual-bootable, I would advise you to keep your Ubuntu partition where it is (or at least the leftmost point as moving that will likely take several hours). What you can do is use gparted (in a terminal run "sudo apt-get install gparted" without quote marks if it is not already installed; also you will need to use a live disk as the filesystem root has to be unmounted) to make a new partition after the Ubuntu partition starting in about the middle of the disk (before middle if you want Mac to have a bigger partition, after middle if you want Ubuntu to have a bigger partition). Format the new Mac partition to HFS+. Then run the Mac OS installation and install to that partition (if the Mac OS installation disk allows you to partition the hard disk from within the installation, skip all the stuff about gparted and partition it there, using the same settings described above).
If you want to permanently remove Ubuntu and just run Mac OS, delete the Ubuntu partition and make the Mac OS partition the first on the hard disk. Format it to HFS+ (again using gparted from a live session) and install the Mac OS to it. Again, if you can format the disk from within the Mac OS installation feel free to do that.
After creating [a] sytem partition(s), your partition scheme is really up to you. This is probably a lot to digest and may not be very clearly worded so please respond again if you have any more questions or need clarification. Such general questions often do not have simple answers.