Is there a partition utility in Ubuntu from which I can break my existing 'ext4' partition into more partition w/o loosing this partition's data?
you can use gparted which can be installed by typing into a terminal
"sudo apt-get install gparted" (without quotes)
and then by either pressing alt-f2 or in a terminal write "gksudo gparted" (without quotes)
gparted help is located here http://gparted.sourceforge.net/help.php
edit: read your modification to the question.
you have to unmount the partition to edit it. also you may use a live cd/usb to edit the partition, too. with same steps.
I think you can,t make another partition because you already have 4 primary partitions. AFAIK is the maximum primary partitions supported, you could make new partitions inside the Extended partition but it is small so...
You would have to delete the swap partition and then shrink the root partition to get space and then make the swap partition again and will need to set the new swap partition in Fstab to be mounted at startup.