Is there any remote control device that works in Linux that I could say Launch mplayer, open my video and play/pause/stop.

Have you looked at lirc ?
See http://sourceforge.net/projects/lirc/

Looks promising. Is there a package in the Ubuntu repos for this?

Of course there is.

You could have answered your question faster by yourself, by asking your package manager. Mine happens to be "Adept", and I just search for lirc and there it is, ready to be installed

I know I know, I am at work however (windoze environment). And I haven't yet installed Kubuntu on my pc (still slackware).

Well, may I suggest that you stop asking theoretical questions, and get on with the job?
This is linux: Jump in. Get merry. Experiment. Be happy.

Then post questions when you have real, rather than imagined problems

Yes... I am jumping in. I have Kubuntu on my laptop to test it out before going ahead with my desktop.

I feel its time to switch from Slackware. I used to be the type to install everything from source and play with the dependencies to get things working. Most of the time I was able to do that. Sometimes I wasn't. I don't have the time anymore for dependencies. I want to just download it, install it and have it working. So I'm trying Kubuntu out. Don't take it the wrong way though, I still love Slackware and continue to use it as my webserver, just not as my day to day desktop.

I guess that is the reason for the theoretical questions. I just want to test the water before "jumping in"

Me too.
But kubuntu 6.06.1(LTS) works well for me (and the 5 other users I provide informal support for).
They are happy, so I am happy. More recent versions have not provided the stability or ease of use that I, and they, require, YMMV
Good luck.