I'd be suprised if Ubuntu didn't include
any \LaTeX stuff at all, so I'm taking a wild guess here: you haven't set up your repositories. IIRC, it can be done by editing /etc/apt/sources.list, running apt-config (both as root), or using synaptic (settings -> repositories).
Be aware of synaptic, though. It maintains a seperate preferences file (this has bitten me once--I hope mentioning this will save you from being bitten by it).
With the long term in mind (and I can't stress enough that we're talking
long term), I would suggest that you learn how to use the command-line tools. Fire up bash, enter apt[tab][tab] (as both root and non-root). Then go briefly over each command with --help and man. That should be enough to get you started.
For viewers:
Code:
$ apt-cache search {xdvi, gpdf, xpdf}
I hope I'm not losing you here
--Jonas
PS. I'm using debian, things might be a little bit different on Ubuntu, but I'm thinking it's not enough to invalidate my advice.