I don't understand how to install widgets in Kubuntu. I download the tar.bz2 file but upon trying to install the files I'll often get a "failed" error. Also for some reason the files are initially filtered by "plasmoid." I'm not sure if I'm doing something completely wrong. Right now I just want to find a different Task Manager widget because the default one is terrible when set up vertifically (the icons constantly shrink).

Wrong board, kwin is not plasma

However it heavily depends on what you downloaded there. tbz / tar.bz2 is a compressed archive, just like a .zip or .rar (or .lha or .arc, if you're older)

You've likely downloaded the sources of a binary plasmoid, what means you got to extract the archive and then compile the plasmoid, what means you want to first check whether k/ubuntu actually has a package for the plasmoid since you frankly don't sound like you've ever used gcc before

Only scripted plasmoids can be installed directly (can be obtained via some get new plasmoids button)

Oh. Thanks. That makes sense. The widget I want to install is http://kde-look.org/content/show.php?content=129291 I'm confused by the installation instructions:

In the main directory run
- cmake -DCMAKE_INSTALL_PREFIX=`kde4-config --prefix`
- make
- make install/strip (as root or: sudo make install/strip )

Where would the main directory be? Doesn't one have to compile the tar.bz2 archive first?

You'd download that file - somehere, let's say your home directory.
Then you open a terminal (konsole), move to that directory and extract the archieve
tar -xjf <filename.tbz>
where "<filename.tbz>" is the name of the file you just downloaded.

It will create a new directory which you subsequently enter:
cd FlexibleTasks
(notice that i've no idea whether that's actually the new diretory name, but it's usually similar to the name of the file you downloaded, except for the leading number, that's a kde-look addition)

There you run those commands. Expect a lot of text and error messages.
=> In order to compile youll require various -dev pacakges such as at least for kdelibs, kde-workspace and Qt - ie. you've to install them from your distro.

Notice that KDE 4.8 got various fixes on the taskbar, so your issues are likely fixed there as well.