You must have a valid registration of the base game in order to install the expansions. If you've lost it and never registered it, you would need to get a new one in order to use the expansions.

30 dollars at gamestop.  Not bad will probally go pick it up. if the expansions are worth it..

any comments on the expansions i played the original non stop a few years back.

I'm also in your position!  I'll probably pick up the new release too, I'm really curious to see how it changed over the years...

Get the Galactic Civilizations 2: Ultimate Edition.  Its all of the expansion packs plus the original game all wrapped up in one neat little package. The one CD key provided with the game activates all the expansions plus the original at once.  Impulse has both the box version and the digital download for $39.99.  The box version is a DVD though so you'd need a DVD drive in your computer.

The expansions add a lot of unique race techs and also allows you to build Terror Stars, which are basically gigantic spheres of doom that blow up stars and their surrounding planets.  Think Death Star only you can't use it as a space station.

I'd say its very much worth it.  Especially considering that both expansions stand alone would cost about $20 each anyway.  Its like you're getting the base game for free.