Installing ubuntu on an Ibook g4 1.42ghz alternate partition... (total inexperience)

I am trying to figure out how to install ubuntu on a partition of my current 100gb hd in my ibook g4 while leaving my Mac os x partition untouched. I am totally inexperienced with linux and cmd lining and have relatively advanced java coding under my belt but otherwise coding illiterate.

I just would like to install the OS with the gui up and running and go from there.

I really appreciate any help anyone has!

I have already been here http://cdimage.ubuntu.com/ports/releases/intrepid/release/ and downloaded the Alternate version which everyone seems to be pointing towards as the best install disc.

Just about to burn it on a cd. Otherwise waiting for some advice. (just about to create the hd partition)

System: 1.42ghz Ibook g4 running currently Mac os 10.5.5 100gb hd. 1.5gb ram

If you have free space, or resized the Macosx partition to make free space on the hd, there should not be a problem with the altenate install. But post if there is.

I use a live disk to resize my partition or you can use disk utility in the mac install disk. First I use Disk Genius to defragment my mac system. Then with the live disk or mac disk I make it the size I want. The rest of the hard disk I leave un formated. Then when you install Ubuntu and come to the point to pick where to install I choose the largest free space. The Ubuntu install will form your boot , swap and root partitions. After you learn more you might want to create another partition to put your home and to share with your mac system. Nown is probably not the time to do it. You will have enough new stuff to learn with just a normal install.