Other disk analyzers are far inferior as they don't allow you to delete files from their interface. The to-ing and fro-ing back and forth between Nautilus and Disk Usage Analyzer is slow, tedious and silly, especially as there is a Linux program that actually does the job properly.
I cannot find kdirstat in Ubuntu Software Center.
kdirstat is a transitional package, you should look for k4dirstat in Software Center
The package is available for Ubuntu 11.10 in PPA - see ppa:jeromerobert/misc
kdirstat was migrated to the new k4dirstat package. I guess that's why you couldn't find it in the software-center.
Anyway, just run the following command in a terminal:
sudo apt-get install k4dirstat
That would install the program in your system. Alternatively, click on k4dirstat 
and it will let you install the program through software-center.
kdirstat is available in Ubuntu 12.04 and 14.04 https://packages.ubuntu.com/search?keywords=kdirstat
kdirstat is not available after 15.10 because it was superseded by k4dirstat (the KDE4 version).
kdirstat is not available in the Ubuntu repos for 11.10 but 11.10 is no-longer supported so that's a non-issue.
You will be able to use it on the next version of Ubuntu apparently but no package was ever made for 11.10.
Do not install packages from 12.04 on your 11.10 system. Upgrade it to 12.04, then before 17.04 gets released upgrade to 14.04
k4dirstatis available in the default repositories. I couldn't findkdirstat, and the download link on their website is broken, so thank goodness for this answer... – Hubro Jun 28 '15 at 13:27